ConcoursMustang Forums
Restoring - General discussions that span across many different groups of years and models => Drivetrain => Topic started by: Angela on November 11, 2015, 11:05:21 AM
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Anyone have (or know of one in a book) a step-by-step process to adjust the idle circuit in a Holley 4150 for the '67 Mustang application? Based on my 67's behavior (described below),
I am suspicious of the idle circuit not being setup correctly. I'm not sure what steps to take to correct the problem. Help appreciated.
*Symptoms*: Car will start and idle quite well. Idles at ~800 rpm in park once the engine is warm. Putting the car into *any* gear will cause the car to immediately stall, unless you apply your foot to the accelerator. If you "nurse" the accelerator to keep the engine running while shifting the car into any gear, the car will then drive quite well at any speed. Coming to a stop, the car will again stall unless you shift into neutral. The car has an automatic transmission.
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Did you go through the process of setting the choke properly, does the motor start and run at 1900 rpm when cold, and when warm idle should be 550 rpm.
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Though I doubt that modifying your Holley is needed to resolve your issue, there is a pretty interesting article in the current (Dec., 2015) edition of Hemmings Muscle Machines about making internal changes to affect the idle circuit.
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Before you make adjustments, make sure you don't have any vacuum leaks. Check the vac lines to the trans, brake booster, and distributor. Also make sure your vacuum advance unit is working properly, and hoses are routed properly.
How far out are your idle mix screws?
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Before you make adjustments, make sure you don't have any vacuum leaks. Check the vac lines to the trans, brake booster, and distributor. Also make sure your vacuum advance unit is working properly, and hoses are routed properly.
How far out are your idle mix screws?
+1 FULL AGREEMENT on this suggestion.
Furthermore, I stand by my comment in your other thread on locating somebody who can tune it up correctly FOR YOU. Old Holley's can be temper-mental if not adjusted perfectly and pretty much, only OLD HOLLEY guys, know them best. Fuels and other conditions have changed so very much over the years, so "going by the book" usually will NOT result in a perfect operating machine on these old big blocks.
Although I understand your hesitation to take your car to somebody you do not know, I cannot help but believe there is NOT a good, reputable fuel-curve specialist in your area that can Dyno this beauty of yours into perfection WITHOUT even having to even drive it on the road. Sometimes the most minor adjustments in combination with other very minor adjustments, you get a car that not only performs as it was originally intended but often you get a car somewhat reasonable on fuel usage.
I consider myself as a good "Carb Guy". I grew up working on very many carbs through the mid 70's and all of the 80's into the 90's when virtually every car made no longer uses them. Good carb guys can be difficult to locate but they are out there. it took me years and years to get GOOD at carburetors. There is no "Easy Answers" book out there to do a quick study that can teach you what takes years and years of experience to learn the ins and outs of on these old baby's. I do not own a Dyno but rest assured, even after I tweak my 67 289 4V to the best I can get it to, I am STILL taking it in to be dyno-checked next...I HIGHLY RECOMMEND THIS if you want the most satisfying driving car you can get. It is worth the money to pay the experts.
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Wow, lots of questions...where do I start?
Well, the car idles around 1500 when cold, then drops to 1000 as it warms up and finally settles around 800 rpm when fully warmed up. Those rpm numbers are with the trans in park. I have no idea what the warm engine idle speed is with the trans in drive, since the engine stalls when I shift into any gear.
I am not sure how I check to ensure the vacuum advance is working.
I will have to check the idle screws and report what I find. I recall setting them to the values specified in the shop manual.
I don't believe I have any vacuum leaks. I have a good Lisle vacuum gauge and I believe I have good vacuum. If someone knows of a specific test I should use, please educate me. As I'm sure you can tell, I am not very educated in the area of these carbs, vacuum and related adjustments.
I appreciate the advice about asking a pro to help me with the carb. Believe me, I would love help. However, I have asked everyone I know and cannot find anyone who knows how to do this.
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Here's an idea on how to take a quick test for a vacuum leak...
While the engine is running, hold your hand over the primary bores of the carburetor (the ones with the choke plate) and with a cupping of your hand over the choke plate (my hand is large enough, small hands maybe not so much) try and choke the engine some and note any change in idle speed or quality. Does the engine pick up speed and seem to smooth out? Does it not make any change at all or run worse? These answers might be clues.
If your engine is warm already, sometimes you can do this with the choke plate too (once the choke heater has warmed enough and is no longer on the high-idle cam) Other times, I have folded a shop rag and laid it over the air intake (ONLY AT IDLE SPEED) to help determine if I might have a vacuum leak. As I said, the changes or NO CHANGE result in idle speed/quality help me to determine if the engine is running lean or running rich
which helps me to decide what might be going wrong. AN EXHAUST GAS ANALYZER TAKES ALL OF THE GUESS WORK OUT, but these suggestions I am talking about are old-school approaches in determining whether you have a rich or lean idle condition.
My guess is you are running lean, usually caused by a vacuum leak and if the carburetor has been built properly it is often at the base gaskets of these 390's, usually a wrong gasket or bad spacer plate but never rule out a brake booster (you can temporarily cap off any vacuum ports going to the booster or other items)
Like I said before, there are so many angles to start with, but to diagnose this, a person needs to know the basics of what might be wrong. The basic question: Is it RICH or is it LEAN.
What city & state do you live in? Maybe somebody here on the forum can come by and take a look.
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Thanks for the advice; I will see if I can replicate your test procedure and report what I find.
Respectfully, I don't understand why people seem to believe my mixture is incorrect, simply because the engine stalls when I shift into a gear. Can someone educate me? The engine runs extremely well once the car is moving.... runs very smoothly and very strong.
Also, if I connect my lisle vacuum gauge, it indicates I have very good vacuum.... i.e. no indication of a leak. Hence I don't know why folks believe I must have a leak.
Again, not trying to be disrespectful, rather I am trying to learn.
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Respectfully, I don't understand why people seem to believe my mixture is incorrect, simply because the engine stalls when I shift into a gear. Can someone educate me? The engine runs extremely well once the car is moving.... runs very smoothly and very strong.
...Also, if I connect my lisle vacuum gauge, it indicates I have very good vacuum.... i.e. no indication of a leak. Hence I don't know why folks believe I must have a leak.
A vacuum leak is not exactly detectable with use of a guage. A vacuum leak can be inside the carburetor too but "outside" sources of a vacuum leak MUST be ruled out first since they are more likely is all I am saying.
Experience is basically impossibly to teach, I don't think anybody feels disrespected about your requests. (at least not me)
What can be ruled out or ruled in with experience might take an experienced person only minutes or moments while under the hood, yet might not ever be capable of figuring out what is actually wrong through typing back & forth on a computer or over a phone call...THAT is the part that makes your request for information difficult.
An example: Nobody can teach my how to play a piano with a book either...some things require a certain "talent" beyond the simpler "understanding how it works" part of the learning curve.
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What is your vacuum at idle ? Has the vacuum modulator on the transmission been known to be good? Also I mentioned about the choke adjustment because I went through a very similar situation with a 390 GT engine with a automatic and it ran strong as yours but floundered at idle and at first in gear and the issue was the choke.
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Respectfully, I don't understand why people seem to believe my mixture is incorrect, simply because the engine stalls when I shift into a gear. Can someone educate me? The engine runs extremely well once the car is moving.... runs very smoothly and very strong.
Also, if I connect my lisle vacuum gauge, it indicates I have very good vacuum.... i.e. no indication of a leak. Hence I don't know why folks believe I must have a leak.
1) The carb has multiple fuel systems, each with their own mixture. There's the idle system, the main system, and the power system. The mixture needs to be correct on each of them, and the transition from one to the next must be correct to prevent stumbling or stalling. Incorrect mixture has been mentioned because it's a common problem, but it's too soon to declare it's what you're experiencing.
2) I have not seen anyone mention that you MUST have a vacuum leak. It's a common problem, and you will not be able to get your carb properly adjusted if you have a leak. What we're saying is that you need to make sure you don't have a leak before you go any further, or you will be wasting your time. Depending on location, a very small leak can have a big impact on how the engine runs. The worst is around the throttle shaft; at the mounting gasket would be significant too. A leak can cause a problem while still giving you a "normal" vacuum reading on a gauge. More importantly, let's say your gauge reads 17" of vacuum. What are you comparing that to? The engine may pull 18" without a leak, but unless you've taken readings previously, you won't know.
The classic way of looking for small leaks is to do a spray test. This involves spraying very small amounts of gas or atomized fluid near the suspected leak while the engine is running, and observing if the engine speed changes. It may increase, or it may decrease - either way indicates a leak nearby. The catch is, you're spraying something highly flammable on a running engine. DANGEROUS, even for those with experience. I usually use carb cleaner or starting fluid, but propane can be used too. Did I mention it's DANGEROUS?
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I usually use carb cleaner or starting fluid, but propane can be used too. Did I mention it's DANGEROUS?
Have used WD40 in the past for some of these investigations - lot less volatile
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I haven't made any further progress on figuring out what is wrong with my 390 stalling (when put into gear) issue. However, to address the question some of you have raised about am I running rich or lean.... is anyone aware of a simple, relatively affordable rich/lean mixture meter? I think some manufacturers refer to these things as "exhaust gas analyzer". Those tools appear to be very expensive and I wouldn't need all the bells-n-whistles they offer.
I don't know any other way to tell if the 390 is running rich or lean, except for removing and checking the color of the plugs. In the case of a 390 in a vintage mustang, I'd rather go to the dentist daily than try and remove spark plugs.
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...how to take a quick test for a vacuum leak...
While the engine is running, hold your hand over the primary bores of the carburetor (the ones with the choke plate) and with a cupping of your hand over the choke plate (my hand is large enough, small hands maybe not so much) try and choke the engine some and note any change in idle speed or quality. Does the engine pick up speed and seem to smooth out? Does it not make any change at all or run worse? These answers might be clues.
If your engine is warm already, sometimes you can do this with the choke plate too (once the choke heater has warmed enough and is no longer on the high-idle cam) Other times, I have folded a shop rag and laid it over the air intake (ONLY AT IDLE SPEED) to help determine if I might have a vacuum leak. As I said, the changes or NO CHANGE result in idle speed/quality help me to determine if the engine is running lean or running rich
which helps me to decide what might be going wrong.
This usually works for me.
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OK, so are you suggesting that IF the engine increases in RPM with your hand held of the choke plate, then the carb is set too LEAN?
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OK, so are you suggesting that IF the engine increases in RPM with your hand held of the choke plate, then the carb is set too LEAN?
Yes, this pretty much holds up to that fact, everything is relevant to what is actually wrong in the first place. I learned basics by means of driving old farm tractors, old pickup trucks and the likes BEFORE things became automated so I guess it could be said that "I get it" easier than others might.
You need to kinda regulate the amount of "choke" you do with your hand, again it is best on a warmed up engine. (You always get the carb "correct" as best possible on a WARM engine before you attempt any actual choke adjustments, choke adjustments are last) See if things improve or at least change by adding fuel, this is done by using the method of "choking", literally by using your hand over the carburetor and watching for a smoothing out of the idle or maybe even a noticeable increase of idle speed. If you notice ANY improvement, this proves it is running lean...THEN by knowing indeed it is actually LEAN can you start eliminating any would-be causes.
I have right now an old Dodge that has a similar problem, it runs almost exactly like what you are describing you have. I KNOW beyond even a shadow of a doubt, it is running lean at idle... and just like your 390, it runs 100% perfect at any speeds away from idle...I just haven't yet run the very tests you need to do to solve the "why" of my problem. My guess for MY problem is that the EGR valve is leaking...Early 390's (in 1967) do not have an EGR valve so you have at least one less possible cause than I have on my old Dodge.
Contrarily, if it is running RICH, the choking method will result in NO CHANGE or a worsening of your idle condition. RICH conditions usually accompany a bit of black exhaust (smoke) or chalking buildup in the tailpipe and/or the smell of raw gas in the exhaust.
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Angela,
When I have had a similar problem I have always started with a vacuum test.
Your car should have a minimum of 17 inches of mercury at 550 rpm idle speed.
Does the car react on the idle screws? If not, it could be a faulty (leaking) power valve.
Also remember that the power valve number should be at least 1.5 inches of mercury lower than the vacuum at the recommended idle speed.
Do you have an original type cam shaft in the car. If not, and it's hotter the symptoms
you have could happen.
Texas Swede
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OK, I finally attempted the experiments suggested in this thread, concerning (a) cupping one's hand over the carb primary and (b) re-checking vacuum at idle.
You guys are amazing... the experiment actually did provide me with some additional information. I have no idea what the following results mean, but maybe someone here can help me further???
* I started the 390 and let it warm up until it would idle.
* Once idling on it's own and the choke plate had fully opened, I cupped my hands over the primary throttle plate. I tried this repeatedly yet couldn't really convince myself doing so had any effect. *If* the engine responded to covering the carb with my hands, the effect was so small that I can't say definitively that it was repeatable.
* However, while idling and warmed up, I pushed forward on the secondary linkage (see photo for details) and noticed a HUGE difference in the way the engine idled!!! I can't say exactly, but I'd estimate the engine RPM increased as much as 100rpm and smoothed out noticeably when I pushed forward on the linkage shown in the photo below. Note that the linkage probably moves forward less than 1/16" (more likely 1/32") yet has the significant effect described above.
What does the above described observation mean? Would what I described cause the previously mentioned stalling when I shift into any gear? What do I do now?
Oh, and the vacuum gauge read 17 inHg at idle. Need on the vacuum gauge was rock steady....never moved.
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The linkage is designed to force the vacuum secondary throttle plates closed when the primary plates close, i.e. when you take your foot off the throttle. There's a little bit of play in your linkage apparently, so when you push on that lever, you're opening the secondary throttle plates slightly, allowing more air into the engine (as they open further, they expose the transfer slots for the secondary idle system, which would then start allowing additional fuel into the engine as well).
The results you describe are consistent with Richard's description of a rich condition at idle.
One question based on your photo:
Is there clearance under the rubber fuel bowl vent valve when the throttle is closed or at idle? There should be, but it's hard to tell from the angle of the photo.
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"Is there clearance under the rubber fuel bowl vent valve when the throttle is closed or at idle?" --> YES, there the rubber stopper raises up above the fuel bowl vent hole when at idle.
Also, I forgot to mention that I checked the idle mixture screws (one on each side of the primary); they're both set to 1.25 turns out. The engine does react when I turn these screws.
*If* the observation I described means my 390 is running rich at idle, (a) what do I do about it? and (b) does that explain why my car stalls when I put it into any gear? I find it difficult to see how the rich mixture explains the stalling...
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Well, after additional reading I suspect that at 1.25 turns out (from fully seated) my idle mixture screws are open too much (rich). I will try turning them in 1/4 turn and restart the car.
However, I'm looking for comments as to whether or not a rich idle mixture could cause an engine to stall when shifting into any gear. I fail to see how this rich mixture could be my issue.
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Am I crazy to suspect my torque converter, instead of the carburetor, as root cause of the car stalling when shifted into any gear? Seems (to me) the torque converter is supposed to allow the engine to continue idling, with very little loss in RPM, while in gear with one's foot on the brakes. In my case, the moment I shift into any gear, the car behaves as though the engine is immediately locked to that gear and stalls. *If* I am able to "feather" the throttle enough to keep the engine running while shifting into gear, I can feel and hear (hearing the rear end locking up?) the drivetrain engaging and usually one or both rear wheels will very briefly chirp.
Could my troubles be a bad torque converter? I cringe at the thought...... because this would mean complete removal of the drivetrain (again)...... and anyone having down this with a 390 knows what a pain this is. On a "daily driver" it wouldn't be so bad I suppose. But in this case I sweat bullets every time I have to remove a bolt, wondering how much time I'll spend trying to make it look like said bolt had never been removed.
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Hi Angela, this all seems very frustrating and i hope you find a solution soon. I have one thing to throw out but not sure it could be the culprit.. There is a secondary throttle stop adjustment under the base plate and I believe your carb has that. This can allow the secondary throttles to stay closed or adjusted to stay slightly open. Unsure if this could be causing a rich running problem but maybe worth a look? I have included a pic of where it would be and it is only accessible from under the carb.
Lastly, I wanted to say what a beautiful engine/carb you have !! So clean!! If you dont mind me asking, where was the carb rebuilt from? I think it looks fantastic!
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I agree that the secondary throttle stop adjustment could play into the mixture being wrong. In my case I'm fairly confident that I have the set screw adjusted properly, merely because the engine responds positively only if I *open* the secondary plates.... allowing more air to enter the engine.... which I think means I'm running too rich.
I'm still very curious to understand more about the torque converter and whether or not that could be my problem. It just seems like something is choking the engine when I engage any gear.... yet isn't the torque converter supposed to isolate the engine from the tranny at idle?
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I've read a number of other posts (outside of this forum) that discuss the same symptoms (stalling when put into gear) and point to the torque converter as root cause. I don't know enough about the torque converter to decide if I agree it could be the problem.
These other posts talk about two issues:
(1) something called a "torque converter clutch" (could this be the lock-up function found only on modern cars?)
(2) a plugged transmission cooler
Again, if anyone can help me rule in or out the torque converter as root cause of my engine stalling, I would appreciate the help.
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I agree that the secondary throttle stop adjustment could play into the mixture being wrong. In my case I'm fairly confident that I have the set screw adjusted properly, merely because the engine responds positively only if I *open* the secondary plates.... allowing more air to enter the engine.... which I think means I'm running too rich.
I may be mistaken, but if you open the secondary plate (or even if they are already open due to the set screw), that will allow more air in... and that air will in turn draw in fuel from the secondary bowl. Won't it? So in my mind that would not necessarily indicate a rich condition, merely that your secondaries are drawing air + fuel as expected.
I would think you would want to cover the secondaries with your hand, which would cut the air and thus any fuel being drawn in there as well. If you cover the secondaries and the car bogs / dies, then you know the secondary plates are not fully closed at idle. Which should be corrected.
Please correct me if my thinking is not right.
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I may be mistaken, but if you open the secondary plate (or even if they are already open due to the set screw), that will allow more air in... and that air will in turn draw in fuel from the secondary bowl. Won't it? So in my mind that would not necessarily indicate a rich condition, merely that your secondaries are drawing air + fuel as expected.
I would think you would want to cover the secondaries with your hand, which would cut the air and thus any fuel being drawn in there as well. If you cover the secondaries and the car bogs / dies, then you know the secondary plates are not fully closed at idle. Which should be corrected.
Please correct me if my thinking is not right.
Along with working on my Holley equipped Mustangs, I have almost fully read David Vizard's How to Super Tune and Modify Holley Carburetors (http://www.amazon.com/gp/product/1934709654?psc=1&redirect=true&ref_=ox_sc_act_title_1&smid=ATVPDKIKX0DER) and believe you to be correct about opening the secondary plate and possibly allowing more fuel. If there are no idle screws on the back, there is no idle circuit back there, only main jets that might get activated by opening the butterflys. There is a possibility of a power valve but I do not believe that would be on a stock carb. But there still might be an issue of it being too rich if either the front or rear float level is set too high, or the power valve is blown out. And yes, there is the possibility that the problem can be non carb related as well. What is the initial timing set at? There should be no vacuum at the distributer at this point. Just trying to re-read the thread and see what has not been checked yet, sorry if I have overlooked something.
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A 4150 Holley idles on all four venturis, so the secondary plate must be adjusted open the proper amount to idle correctly. Generally, with the carb linkage "closed", the secondary butterflies should be open just enough to see the idle transfer slot. It should look like a square, meaning the amount of the slot visible should be as high as the slot is wide.
One way to know whether the secondary butterflies are open at least in the ball park is that you should be able to adjust the idle stop screw to obtain a proper idle speed and still have no vacuum at the ported vacuum opening in the primary metering block. If you have vacuum here, then the secondary is not open enough and not contributing to the idle speed as it should.
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A 4150 Holley idles on all four venturis, so the secondary plate must be adjusted open the proper amount to idle correctly. Generally, with the carb linkage "closed", the secondary butterflies should be open just enough to see the idle transfer slot. It should look like a square, meaning the amount of the slot visible should be as high as the slot is wide.
One way to know whether the secondary butterflies are open at least in the ball park is that you should be able to adjust the idle stop screw to obtain a proper idle speed and still have no vacuum at the ported vacuum opening in the primary metering block. If you have vacuum here, then the secondary is not open enough and not contributing to the idle speed as it should.
This seems to be a key piece of information I didn't know, thanks for the post.
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Here's what I think I heard from the last several responses:
#1 I should cover the secondary opening with my hands and see if the engine reacts in any way. I'm 90% certain I already did so and the engine did NOT react. I'll double check by repeating this test
#2 Next, I should see if I have vacuum at the carb vacuum port when idling at the proper idle speed. If the secondary stop set screw is where it should be, I should not have vacuum at idle (at the carb vac port), correct?
#3 I should attempt leaning my idle mixture screws 1/4 turn (turn them IN) and see if it helps. They are presently set at 1.25 turns out from seated.
Also, I have seen any comments concerning my question about the torque converter being root cause of the stalling. I finally got a hold of the guy who rebuilt my transmission and sold me the rebuilt fomoco torque converter. I explained the symptoms and he stated they could indeed be caused by the torque converter. I could scream. The thought of tearing apart a concours restored car makes me nauseous. If anyone has suggestions about the best way to swap a torque converter in a car you don't want to scratch anything, please let me know. Thanks.
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Re #2, yes.
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A 4150 Holley idles on all four venturis, so the secondary plate must be adjusted open the proper amount to idle correctly. Generally, with the carb linkage "closed", the secondary butterflies should be open just enough to see the idle transfer slot. It should look like a square, meaning the amount of the slot visible should be as high as the slot is wide.
One way to know whether the secondary butterflies are open at least in the ball park is that you should be able to adjust the idle stop screw to obtain a proper idle speed and still have no vacuum at the ported vacuum opening in the primary metering block. If you have vacuum here, then the secondary is not open enough and not contributing to the idle speed as it should.
I looked at holley's info and they are saying to adjust the secondary stop screw to just touching and then 1/4 turn. Looking at my carb the secondary slots are at two different heights and what looks to be up the venturi a good ways so to uncover one would open the butterfly what seems to be too much. I cant seem to find info to read up on this.
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To check vacuum during idle, should I use the vacuum port at the rear of the intake manifold spacer, which I believe normally connects to the transmission modulator -OR- should I connect my vacuum gauge to the vacuum port at the front of the carb, which normally connects to the distributor?
Aside from simply verifying I do or do not have vacuum during idle, should I do anything else while running the engine with the vacuum gauge connected?
For example, I plan to slightly lean the idle mixture from the present setting of 1.25 turns (from fully seated) to 1 turn. Should I be adjusting these idle mixture screws based on vacuum gauge readings? I don't know if the two things are related (idle mixture screw position and vacuum gauge readings)
Thanks
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Vacuum gauge goes to the ported vacuum on the primary metering block (front of carb). There is a technique to adjust spark advance for best vacuum but I'm not sure that adjusting the idle screws will give you any insight into the mixture.
You can see the secondary transfer slot in this picture I found on the Internet. It is #2 in this picture.
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Vacuum gauge goes to the ported vacuum on the primary metering block (front of carb).
A C7OF-D carb, which is the one in question if I'm not mistaken, doesn't have that port. If present, it would be the same as manifold vacuum, which is what you want to look at when adjusting idle.
Not to be confused with the side port, which is venturi vacuum.
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I'm referring to the vacuum you would read to determine proper adjustment of the secondary butterflies. Same vacuum source that would go to the distributor vacuum advance.
Yes, manifold vacuum to adjust timing using the vacuum method.
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You guys have lost me....totally. "manifold vacuum", "side vacuum", "metering block vacuum port". I'm lost. Where are these ports? Are they truly measuring *different* vacuum???
To the comment that suggested it may not make sense to monitor vacuum while adjusting the idle mixture screws..... personally, I haven't a clue. However, reading David Vizard's "How to Super Tune and Modify Holley Carburetors" book, the author specifically states to use a vacuum gauge while adjusting the idle mixture screws. He says that when adjusted properly, there shouldn't be any vacuum at the carb when idling. --> Hence my question about where to plug in my vacuum gauge.
Help? I'm lost, based on the above posts.
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You guys have lost me....totally. "manifold vacuum", "side vacuum", "metering block vacuum port". I'm lost. Where are these ports? Are they truly measuring *different* vacuum???
To the comment that suggested it may not make sense to monitor vacuum while adjusting the idle mixture screws..... personally, I haven't a clue. However, reading David Vizard's "How to Super Tune and Modify Holley Carburetors" book, the author specifically states to use a vacuum gauge while adjusting the idle mixture screws. He says that when adjusted properly, there shouldn't be any vacuum at the carb when idling. --> Hence my question about where to plug in my vacuum gauge.
Help? I'm lost, based on the above posts.
There are two main vacuum signals to consider when working with carburetors:
Venturi vacuum is the amount of vacuum present in the main venturis. When the butterflies are closed at isle, there is little airflow through the main venturi, and the vacuum reading is low. As the butterflies open up, airflow increases, and venturi vacuum increases. This signal is usually used to advance the spark. On a 4150C carb, venturi vacuum is available on the side of the carb, at the 90 degree brass fitting (photo).
Manifold vacuum for the most part behaves inversely to venuri vacuum.It is a measure of the manifold vacuum below the throttle plates. At idle, with the butterflies closed, there is little airflow through the carb, so the vacuum is strong due to the pistons trying to suck air out of the manifold. As the butterflies open, air (and fuel) rush into the manifold, so the manifold vacuum drops off. Manifold vacuum is available at various places on the intake manifold, or on some carbs there's a port coming out below the throttle plates as rockhouse66 pointed out. C7OF-Ds & various other Holleys used by Ford don't have this port.
Your quote from Vizard is correct - at idle, venturi vacuum is low, manifold vacuum is high. I've not heard of using venturi vacuum to optimize idle, but there are other people here more qualified to comment on that.
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Thanks! Your explanation is helpful and makes sense to me. In my application, I am aware of two vacuum ports at/near the carb: (1) passenger side front of carb, routing to the distributor and (2) underneath the carb at the carb spacer, routing to the transmission.
I'll check vacuum readings at both locations noted here. I think I should watch the vacuum value at location #1, while I adjust the idle mixture screws. Correct me if that's incorrect.
Another related question, could my stalling condition have anything to do with the vacuum provided from the carb spacer to the transmission? I have no idea what the vacuum sent to the trans is used for.
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Angela, have you removed a spark plug to check the color yet? That should determine if you're rich or lean.
There are MANY things that could be an issue. Timing is more forgiving at RPM that it is at idle.
If it is an original, you could have the issues I did with the dual quads on my Shelby. The throttle shafts were worn, which makes for a piss poor idle. If memory serves me correctly you have power brakes, so is the booster leaking?
Another possibility would be the metering block and contaminates in the emulsion tubes. Very common in older carbs, especially if they have set for a length of time.
As for San Jose's comment: You have NO idea how hard it is to get a competent person who knows Holleys inside out.
I have a pointer for you if you can't resolve the issue. At least he'll be able to rule out the carb being the culprit. He's from So Ca, like I am. However, he is now in Austin, Tx. I am sure he'd treat you right if you sent it to him and had him rebuild and do the dry spec set up.
-Keith
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Hi Angela, Just read through your thread, and thought I'd offer my opinion. I've got a lot of experience with Holleys and tuning in general. It's a shame your not near Philadelphia, Pa as I'm sure we could get you straightened out in short order. It's really hard to diagnose a car without seeing it firsthand, but here's a few things to consider......
1st, about your trans question, although it's possible that you could have a converter issue that's causing it, It's HIGHLY unlikely with a C6 like you've got. It's more prevalent in newer cars with a lockup clutch in the converter but it's still rare.
Although it's possible that it's an issue with the ignition system, that's also highly unlikely, assuming the car idles in park.
As for a Vacuum leak, since you have 17" of vacuum at idle, any leak is pretty small, and shouldn't cause your stalling.
A couple questions,
Does your car instantly and abruptly stall as soon as you put it in gear, or does it kind of stumble first ?
If you bring the RPM's up to about 1500/2000 then put it in gear, does it still stall ?
Can you drive the car, if so, how does it run at speed ?
Since it's kind of pointing to a carb issue, Here's a few things to check...
Do the mixture screws seem to affect the idle ? , will the car stall when you run one or both screws all the way in ?
I'd back the screws out about 3 turns or so and se if it still stalls. 3 turns should be pretty rich, but your car won't stall because of this and it will rule out the mixture adjustment.
Holleys are pretty simple, basic carbs, but they can still drive you nut's if they have issues..
If the car' still stalling in gear (and it's a carb issue) it's either really lean or really rich. Really lean could be caused by an internal carb issue but that's pretty unlikely. Because closing the choke (or cupping your hands over the carb) doesn't change anything and you get some improvement and an increased idle by cracking the secondary's, they both point to a REALLY rich carb condition. This is usually caused by one of two things on a Holley, Dripping boosters or and internal leak.
1st, start the car and look down the carb throats. see if you can see fuel dripping from the boosters onto the throttle plates. If you do, it's usually caused by your float adjustment being too high. Other causes can be a needle/seat issue, a float issue (binding or full of fuel), or fuel pressure too high.
If you see no evidence of fuel dripping from the boosters, I'd highly suspect an internal leak into the power valve well in the main body, either from a blown power valve (unlikely) or a warped metering block or main body (REALLY common on older Holleys)
If you're not comfortable with taking your carb apart, I'd try and borrow a known good Holley just to make sure your carb is your problem, then send your carb back to whomever rebuilt it or to a known good carb guy..
If you are comfortable in dissembling your carb. Drain the front fuel bowl into a cup or rag by removing a lower bowl screw (you can leave the carb on the engine.) carefully remove the front bowl and the front metering block. You should see a well (recess) in the carb body where the power valve sits. This well is connected directly to manifold vacuum and any fuel that leaks into here gets sucked directly into the engine. The well should be dry, If it's wet, either the power valve is bad, not common, or the main body or metering block is warped. This is REALLY common with old holleys, as when the gaskets get old and leak, people tend to get king kong to tighten the float bowl screws to try and stop the leak. This causes the 4 corners of the main body where the bowl screws thread into to bow up and fuel to leak between the block and the main body and get drawn into the engine. You can check the main body and the metering block with a straight edge. If the block is warped, find another one, if the main body is warped (LIKELY) You can either have it milled flat, or spend about 1/2 hour with a sharp, wide, fine flat file and do it by hand. You'll have to take the carb off the engine, completely disassemble it, and clean it really well afterwards. Use a new power valve and a new power valve gasket.
At least 1/2 of the old Holleys I rebuild have at least some degree of distortion of the main body, warping a block is uncommon but you do find it occasionally.
Once you get the stalling thing fixed, you can use your vacuum gage to set your mixture screws. Start with 1 1/2 turns out and adjust each screw for the highest vacuum reading.
Let us know how you make out,
John
BTW, If you do find out your stalling was caused by your carb dumping fuel into the intake, make sure you change your oil, as a lot of the fuel will end up in the pan...
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70cj428, where around Philadelphia are you located ?
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70CJ, you and a few others are the odd balls. I do the basics, but there are few who have spent time mastering the intricacies of multiple Holley carburetion in this day and age. The side draft Mukunis on my Datsun SSS 510 and 2000 Roadster was even more difficult to get dialed in.
-Keith
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70CJ - wow, thanks for the detailed write-up. I appreciate everyone's comments & advice.
I still have no idea what's wrong with the car. I think I've tried everything that folks have suggested
I recently spoke with someone who claims to have run across the exact same issue with his 390 C6. Here's what I was told:
(1) His car behaved exactly as mine: immediately stalling upon shifting into any gear. It would run perfectly, *if* you could successfully feather the throttle while shifting into gear, which would keep the car running long enough to get it moving. Once moving, it would drive perfectly.
(2) He was told by the shop who rebuilt his tranny that the torque converter must be bad. They swapped the torque converter... and the problem remained exactly the same.
(3) The transmission rebuilder then said the problem could be with the valve body. The removed the valve body and said that it "was trying to enable drive and reverse at the same time". They rebuilt the valve body and reinstalled it. The car now works perfectly.... no more stalling.
Does any of that sound believable? If there's even a shred of truth to this, I would MUCH prefer to first try swapping my valve body before tearing apart the entire drivetrain to get at the TC. According to my invoice from the trans shop, the valve body in my 1967 C6 was replaced with a "68 valve body recall/update" when it was rebuilt - my point being that the part was touched and errors are made....it could have been rebuilt incorrectly.
Thoughts?
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According to my invoice from the trans shop, the valve body in my 1967 C6 was replaced with a "68 valve body recall/update" when it was rebuilt - my point being that the part was touched and errors are made....it could have been rebuilt incorrectly.
Thoughts?
Going back through the entire discussion, I didn't see any mention of transmission work. That's the sort of information that could be really helpful in working through the problem. Is there anything else that you haven't mentioned? Perhaps it would be best to go back to the beginning:
- When was the last time the car functioned properly?
- What has changed since then? That includes elapsed time, work that's been done, exposure to unusual weather conditions - anything you can think of.
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Going back through the entire discussion, I didn't see any mention of transmission work. That's the sort of information that could be really helpful in working through the problem. Is there anything else that you haven't mentioned? Perhaps it would be best to go back to the beginning:
When was the last time the car functioned properly?
What has changed since then? That includes elapsed time, work that's been done, exposure to unusual weather conditions - anything you can think of.
----> Sorry about that. I really thought I had explained the entire situation. The car has been in the process of being restored.... it has been apart and off the road for at least 15yrs. When was the last time the car functioned properly? At least 15yrs ago... it hasn't been assembled enough to attempt driving until recently. What has changed since then? EVERYTHING. Every single nut, bolt, washer and screw has been removed, restored and reinstalled. The transmission rebuild was farmed out to a pro, as was the engine machine work.
We've discussed the carb and transmission as main culprits in this thread. Pertinent to those two items, the entire tranny, including the TC, was rebuilt top to bottom. The carb was sent out to Pony Carbs (at least 5yrs ago, before the owner died) where it was replated and rebuilt. Since the very first day the drivetrain was installed in the car, it has behaved as described (stalling when shifted into ANY gear).
Let me know if the above description helps.
As far as I am concerned, I am looking for another valve body to swap in, before I even consider tearing half the car apart to get at the TC. Thus far I haven't been able to find another fomoco TC.
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Let me know if the above description helps.
Yes, it does. It gives a better view of the range of potential issues you could be dealing with. For example, if the car had run normally a year ago, and then the carb was rebuilt and the problem started, it would make most sense to concentrate on the carb, or possibly deteriorated gasoline. But this widens the scope to potential transmission issues.
The two most likely candidates are carb or transmission. It would help to narrow the problem to one of the two. (But don't rule out the possibility that there are problems with BOTH!) It's impractical to swap the transmission, but the carb is reasonably portable. Running your carb on another similar engine/trans combination, and/or installing a known good carb into your vehicle would potentially narrow the search. If your carb runs fine on another engine, you're probably dealing with a transmission issue. If your carb fails on another engine, you've got carb issues (but maybe trans problems too). You get where I'm going with this. Once you determine which system is at fault, you can start narrowing down to a specific cause.
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I still see no mention of checking the plugs for color. What not one single person has mentioned other than a possible vacuum leak is the fact FE intakes can be prone to leaks at the intake gaskets. If you mill the heads more than .020 the intake has to be cut as well. The Felpro performance intake set is also known for issues. They have been known to become soft with oil and get sucked into the intake ports when they become compromised, often leading to coolant/oil use. putting a 96lb intake isn't easy to get down right, as it's also easy to misalign or have the gaskets shift. Did you check the intake with a straight edge?
As for Pony carbs, I know of several who are less than happy with them as well. I won't bother with my experience here with the BJ/BK's for my vehicle.
I gather the rebuilt unit also sat around for several years. Pony claims they run them before they are shipped back to the customer, which would mean gaskets and the power valve may have been compromised because there was fuel run through the unit post rebuild. Did you check the modulator for ATF? I have also seen the modulator diaphragm go bad, which not only leaves you with a vacuum leak, but they often suck ATF through the unit and back into the engine.
The diaphragm on the distributor can be checked easily. You can check it with a mighty vac. When you pull vacuum on the diaphragm, it should hold that vacuum until you release it.
As Dave mentioned, you have three circuits to deal with. Many possibilities, even thermactor control issues.
-Keith
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Keith - plugs are the correct color, sorry for failing to mention that. I checked them day #1 when the problem first exhibited itself. I'm not pulling the plugs again... :-) it's a nightmare to do in a 67 390.
As far as vacuum leaks.... I stated I have measured vacuum multiple times with a Lisle gauge....17 inHg...right on the money.... hence, *if* there's a leak, it's tiny IMHO.
Concerning the carb - like I said, the problem has been here since day #1.... so whatever the issue is, it's not from sitting. Frustrating!
WT8095: I agree with you in that it would be excellent to swap in a known good carb. Sadly, I don't own any other known good carbs.
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I know your pain, Angela. I have a '67 GT500. The two to the left rear are the worst. If you're short, I am sure it's even more fun.. ( Yes, I am being sarcastic) I have had three back surgeries, so I understand from another aspect. ;D
I have seen many of the emulsion tubes get fouled with the crusty white remnants of fuel. I have two four barrels, and I learned very quickly that even though I am proficient at one, two changes everything.
If I were closer I'd volunteer to assist.
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As far as vacuum leaks.... I stated I have measured vacuum multiple times with a Lisle gauge....17 inHg...right on the money.... hence, *if* there's a leak, it's tiny IMHO.
It doesn't have to be a big leak to make a difference in mixture. It's worth the time to check all of the likely spots everyone has suggested, and it can be done inexpensively and without taking things apart. Honestly, this should be part of a preventative maintenance routine once the car is up and running - vacuum hoses crack and loosen up, diaphragms and gaskets develop leaks, etc. Could be a once a year or every other year sort of thing.
WT8095: I agree with you in that it would be excellent to swap in a known good carb. Sadly, I don't own any other known good carbs.
Yeah I didn't expect that would be an easy one to do. But it was SO easy for me to suggest! ;) ;D ::)
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I looked for vacuum leaks but found nothing. Vacuum reading remains steady at 17 inHg.
I'm still searching for a valve body and torque converter.... So, in the meantime, I experimented with the carb a little more. Here's what I did:
Turned the idle mixtures screws IN 1/4 turn (which left the setting at 1 full turn out from seated position)
Started the car, feathered the throttle until the engine warmed up
Car would not idle.... stalled without opening throttle slightly. (the engine did idle with the previous idle mixture setting of 1.25 turns out from seated)
Turned the idle mixture screws back out to 1.125 turns from seated
Restarted car
engine idled at 850 rpm.
Attempts to lower idle from 850 cause the engine to stall
Idling at 850 rpm, I tried to shift into reverse. Engine stalls in 1 second
Idling at 850 rpm, I tried to shift into drive. Engine stalls in 1 second
I need a known-good carb to swap in and test. I have several good cores for this (390) application, yet I'm not good at rebuilding them. Anyone out there good at rebuilding these carbs?
Anyone have a known-good holley for this application they want to consider selling?
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"For Testing Purpose Only", there are many, many carbs you could try and often times a "Buddy" close by has one available. Just make every attempt to not alter things while making this "test", use a flexible fuel line, leave the throttle linkage alone or build a temporary linkage, do not worry about the choke system, things along thos lines.
If your "test carb" does the same symptoms, maybe your thought on the transmission are more likely then. Personally, your description matches a carb problem but I cannot hear or "feel" what is going on with the car while typing on a keyboard.
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Hi Angela,
Haven't been spending much time on the computer recently, wondering how you made out....
A couple thoughts on the transmission...
The only thing I can think of (internally) that would cause a C6 to lock up when you put it in drive would be if the direct clutch was applied on when the trans went into low, which is possible with a valve body problem but REALLY unlikely, and the car probably wouldn't upshift normally after you got it moving. (you said in your first post that you could feather the gas and get the car moving, then it drove normally) Additionally, it would self destruct in short order...
You could have something wrong internally with the torque converter, but that would also be very uncommon with a C6, and it the converter was locked up, the car would probably stall almost instantly when you put it in gear. ( It sounds like it takes a second or 2 to die) I actually had that happen once with a C4 converter, the converter company found a nut inside the converter that must have fallen in before the converter was installed.
Is there any way you could post a video of it running , then stalling ? As dumb as that sounds that would be pretty helpful.
I still thing it's a carb issue...
It's a shame that you're not near PA, I'm sure we could get you up and running in short order..
John
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Thanks John. Hmmmmm, a video..... I could give that a shot.... not sure how well the sound might turn out. Interesting idea. To be honest, I suspect she stalls in 1 second or less..... it doesn't really idle for any length of time. I want to hold out hope that it's the carb or the valve body, yet it really seems like the torque converter is the culprit. I could cry. The thought of removing 100 bolts, the hood and a million other parts is just sickening. Trying to make it look like those parts were only installed once would be very difficult.
I think I should try posting a wanted ad for someone who could rebuild one of my other carbs. I have quite a few 9510-D and -B carbs... but they all need rebuilding and I'm apparently no good at it. Plus, I still cannot locate a 67 or 68 torque converter or a valve body. Ugh.
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this guy is supposed to be a holley guru. check him out. joe bunetic
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Thanks John. Hmmmmm, a video..... I could give that a shot.... not sure how well the sound might turn out. Interesting idea. To be honest, I suspect she stalls in 1 second or less..... it doesn't really idle for any length of time. I want to hold out hope that it's the carb or the valve body, yet it really seems like the torque converter is the culprit. I could cry. The thought of removing 100 bolts, the hood and a million other parts is just sickening. Trying to make it look like those parts were only installed once would be very difficult.
I think I should try posting a wanted ad for someone who could rebuild one of my other carbs. I have quite a few 9510-D and -B carbs... but they all need rebuilding and I'm apparently no good at it. Plus, I still cannot locate a 67 or 68 torque converter or a valve body. Ugh.
You do not need to pull the engine to change the torque converter. With a C6 a transmission jack would be a must. Good luck.
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this guy is supposed to be a holley guru. check him out. joe bunetic
Charles, very interesting. Thanks for the tip. I'll give Joe a call
Ruppstang, could you elaborate? I assume you're implying that one could alternatively remove the driveshaft and exhaust, then slide the transmission away from the engine, yes? Hmmmmm, I wonder how difficult it is to reach all of the bolts between the engine and transmission. I'll take a look and ponder this.... thanks.
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Yes that is exactly what I am saying. It is done in transmission shops every day. You may be better of taking it to a shop that has all of the equipment.
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Could someone please explain what could possibly fail (or be incorrectly adjusted) in a Holley 4150 such that it causes the symptoms I have described? My engine idles well and drives well (if you can keep it from stalling), yet immediately stalls upon shifting into any gear. I simply do not understand what, specifically, carburetor problem would cause this symptom.
I spoke with Joe about having a second carb rebuilt, yet he warned me that any rebuilt carb is going to require adjustments on the engine, hence there's no way to ensure the engine will initially run any better than with my existing carb. Therefore, I want to understand the mechanism by which you guys think my carb is messing up all of my fun. :-) I just don't get it...
Help?
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"For Testing Purpose Only", there are many, many carbs you could try and often times a "Buddy" close by has one available. Just make every attempt to not alter things while making this "test", use a flexible fuel line, leave the throttle linkage alone or build a temporary linkage, do not worry about the choke system, things along those ideas.
If your "test carb" does the same symptoms, maybe your thought on the transmission are more likely then. Personally, your description matches a carb problem but I cannot hear or "feel" what is going on with the car while typing on a keyboard.
This is why I suggested a "KNOWN GOOD USED CARB" (though I didn't come right out in my previous comment and say that, I suppose)
The "borrowed", known to be good donor could be something like an AFB or modern version holley or something with the same carb base only, nothing specific or "exact" as you have.
By using another "known good" (borrowed?) carb, you will answer at least the main question, "Is it my carb or my trans?"
This should be possible by ONLY buying a couple of base gaskets and possibly a few feet of 5/16" rubber hose.
I did this VERY SAME THING several years ago when I tried to fix my old Holley I was then using on my 289. I rebuilt it, It wouldn't idle...no good, I had my older brother rebuild it too...still, the same problem...no good. I tried another (different) carb...BINGO, it's a bad carb. I never figured out "why", I simply switched carbs since 2 different builders couldn't nab the problem AND I needed the car for work. Normally, neither of us have troubles building carbs...but, big difference at the time... I wasn't trying to be Concours. I simply wanted to drive the car. Mine is supposed to have a 4300 Autolite on it...Those are notoriously BAD! At least if you figure out what is wrong (carb or trans), you can get going on the right "Concours correct" solution.
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I understand and respect the suggestion to try using a "known good carb". In words, that sounds simple and straightforward. In practice, however, it's not. I've contacted everyone I know (in the hobby or even remotely related) within a couple hour drive and cannot locate a carb (ford, holley or other) that is sitting on a working engine.
Even if I could find a known-good-carb, the next hurdle is getting the owner to let me remove it from their engine.
Fundamentally, IMHO I think the issue is that once fuel has been run through a rebuilt carb, the carb needs new gaskets if not used within a few months. I believe that's why no one has a carb laying around I can use.
Therefore, I thought I'd go back and try to understand the carb problem that many people think is causing my stalling issue. I don't understand the mechanism.
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There are SO MANY passages in items like metering blocks as well as the main body of the carb itself and describing how they all work together on any one specific example of a Holley carburetor is I feel fundamentally impossible (using words). This is where somebody who has beat their head in before with the EXACT problem you have, survived the head trauma and actually fixed the problem, before provebially "throwing the carburetor through a windshield of another car" (within throwing distance) comes into play.
Maybe send or take yours to another running car with another FE engine in it? Put your carb on another engine? See if the problem follows the carburetor?
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Angela:
A point I made when we first broached the subject and the length of time post rebuild. I am not impressed with Pony Carburetor either. They didn't want to do a set of BJ-BK's. A Holley is a Holley. They claim to run the rebuilt carburetors on an engine post rebuild. If that is the case, the gaskets would be compromised in just a few months of sitting.
Because of the alcohol content in current fuels, I have seen the fuel turn white and crusty in passages in a short time as well. Did you think about contacting Pony and seeing if you could send it back to them and let them inspect it being they rebuilt it. If they are running and adjusting them, it shouldn't be a big issue to sort your carb out.
Call them, you have nothing to lose. P.S. It doesn't have to be an FE you run it on.
-Keith
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Angela:
A point I made when we first broached the subject and the length of time post rebuild. I am not impressed with Pony Carburetor either. They didn't want to do a set of BJ-BK's. A Holley is a Holley. They claim to run the rebuilt carburetors on an engine post rebuild. If that is the case, the gaskets would be compromised in just a few months of sitting.
Because of the alcohol content in current fuels, I have seen the fuel turn white and crusty in passages in a short time as well. Did you think about contacting Pony and seeing if you could send it back to them and let them inspect it being they rebuilt it. If they are running and adjusting them, it shouldn't be a big issue to sort your carb out.
Call them, you have nothing to lose. P.S. It doesn't have to be an FE you run it on.
-Keith
Keith, you have been out of the loop, Jon of Pony Carbs passed away 3 or 4 years ago. the business closed shortly after.
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Bob,
I wasn't aware of his passing. I had two experiences with him, which left me less that enthralled. I guess that rules out that suggestion.
Here is another with a stellar reputation.
Angela, he does a lot of work for the guys on the 428 Cobra Jet site.
Chris's Carb Shop
email is chriss.carb.shop@hotmail.com
Phone (937)890-0970
Toll free 1-877-498-2272
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Angela:
A point I made when we first broached the subject and the length of time post rebuild. I am not impressed with Pony Carburetor either. They didn't want to do a set of BJ-BK's. A Holley is a Holley. They claim to run the rebuilt carburetors on an engine post rebuild. If that is the case, the gaskets would be compromised in just a few months of sitting.
Because of the alcohol content in current fuels, I have seen the fuel turn white and crusty in passages in a short time as well. Did you think about contacting Pony and seeing if you could send it back to them and let them inspect it being they rebuilt it. If they are running and adjusting them, it shouldn't be a big issue to sort your carb out.
Call them, you have nothing to lose. P.S. It doesn't have to be an FE you run it on.
-Keith
Keith, you have been out of the loop, Jon of Pony Carbs passed away 3 or 4 years ago. the business closed shortly after.
At the MCA Concord, CA car show (2006 or 7 I think), Jon had did several demonstrations. The testing subject was brought up and Jon said the carburetors were tested on an engine, drained and new gaskets were included for shipping. Someone asked about the drained gas and Jon was a bit "miffed" at the subject being brought up again (words like - "Didn't you hear what I said?").
I had three 4100 carburetors rebuilt by Pony Carbs, two were mine, one was a no core purchase. All three were installed without any problems.
Jim
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Well, as you may have noted from the discussion: She didn't mention a gasket change. The brown style Holley gaskets are notorious for drying out sitting, especially if they have seen fuel. Fuel sitting for an extended time tends to turn into a white chalky substance.
Jon would not do BK-BK carbs. That speaks volumes in my book, and trying to convince me there was some voodoo when doing them was what justified my commentary.
The PO had the carb done, Pony has been gone since about 2011. So the question is: How many years ago was it done? Did the PO replace the gaskets? If so, how long ago.
I think we've covered most of the common sense scenarios, and at this juncture the carb is suspect.
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U P D A T E:
I FINALLY found someone with another holley I could try on my 390. A friend of a friend let me borrow the holley (aftermarket) that was working perfectly on his '70 Mustang. The fuel inlets were on the opposite side of the carb and fuel was directly fed to the secondary, so that complicated getting this carb setup in my '67. But...
When I finally got this known-working carb situated onto my 390, she fired right up and idled. I could hardly believe it. I didn't change any of the idle mixture screws... I just bolted it up and my 390 idled. I let 'er warm up and then attempted to put 'er into reverse and drive...
IT WORKS!!! I cannot believe this!!! Using this borrowed carb, my 390 will now idle perfectly in drive and reverse.... no stalling when in gear! Crazy!
An additional bonus, using this borrowed carb, my 390 idles 150 RPM slower than I have EVER been able to get it to idle (700 VS 850)!
SO, I'd like to know what you guys recommend, should I
(a) Find someone to rebuild the ford-holley 9510-D that's been giving me trouble since I had it professionally rebuilt (and replated) many years ago?
(b) OR, should I find someone to rebuild an identically dated 9510-D spare carb I own?
Option (a) concerns me because that carb has been giving me so much trouble for many years. Even after the professional rebuild, I personally put a rebuild kit (gaskets, power valve, float needles etc) only to find it still behaved the same way). There must be something fundamentally messed up with that carb. I think I'd prefer to start with a different candidate, yet would like some input.
Finally, I still have NO CLUE what on earth goes wrong with a carb such that it causes an engine to idle, yet stalls when shifted into gear. I wish I could understand this.
Thanks to everyone for continuing to push on me to find another carb to try. I kind thought everyone was nuts. Turns out you guys were onto something. Thanks a million! I don't need to yank the drivetrain to replace the torque converter!!!!!!!!!!!
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IT WORKS!!! I cannot believe this!!! Using this borrowed carb, my 390 will now idle perfectly in drive and reverse.... no stalling when in gear! Crazy!
An additional bonus, using this borrowed carb, my 390 idles 150 RPM slower than I have EVER been able to get it to idle (700 VS 850)!
Congratulations! I can only imagine the huge smile on your face when it worked ;D
Briefly, I think the two most likely issues with the problem carb are either the secondary throttle plate adjustment not being quite right, or air leaking around worn throttle shaft(s). Some carbs can be repaired by installing throttle shaft bushings (I've done this myself), but I am not yet familiar enough with 4150s to tell you if that's feasible or practical in this case. There certainly could be other issues as well, and in stubborn troubleshooting situations it's not surprising that multiple things are wrong, making diagnosis very difficult.
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It is really good to hear that you were able to finally figure this one out. I am not at all surprised it ended up being the carburetor. I have thought this all along.
As many have suggested already, these carburetors are very tricky. That being said there are people who can work on them and repair your original carburetor. Hopefully somebody will chime in very soon who has had recent good experience with a Rebuilder that can take what you have and find out what exactly is wrong with it. More often than not, a passageway is plugged or something is warped or something is worn out. Somebody with very good experience with you particular model of carburetor can figure this out.
What a relief this must be for you to know this now. Ever now and again we need to make progress :D
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If money and time were no object, I would try to find a rebuilder that has a working test engine. Have the problem carburetor tested, as is, to verify that your stalling condition is transferred to his test engine....then start swapping out components. Once the right, or wrong, piece is swapped out, you will have confirmation that the stalling condition has been resolved.....Although if you found a good rebuilder, they may already know what the root cause of the stalling condition is. I have been on the side-lines listening to this discussion...as I have a 390 GT that has not been running for more than 25 years.
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Option (a) concerns me because that carb has been giving me so much trouble for many years. Even after the professional rebuild, I personally put a rebuild kit (gaskets, power valve, float needles etc) only to find it still behaved the same way). There must be something fundamentally messed up with that carb. I think I'd prefer to start with a different candidate, yet would like some input.
Finally, I still have NO CLUE what on earth goes wrong with a carb such that it causes an engine to idle, yet stalls when shifted into gear. I wish I could understand this.
Hi Angela. You seem smart and carbs are not that hard if you learn the basics. It's imperative that you are able to test the circuits of the carburetor or it's a guessing game. Warped parts are common because the screws do not need to be tight, just barely snug, and most people have over torqued the screws which causes internal and external air and fuel leaks.
The reason the car would stall in gear is that engine is loaded and needs more volume of the correct air fuel mixture to run, since the engine is asked to do more work. The problem with your existing carburetor could be the wrong base plate, bent idle screws, bent butterflies or the wrong idle screws we're used at some point and forced into the seat which damaged the port.
My guess is that there is debris in the bottom of the float bowl which is not allowing enough fuel to be drawn in to the carburetor at idle. When the engine was running in neutral I can guess it was running poorly and light popping could be heard which can indicate a lean burn misfire. Lean burn misfires can water the eyes where a rich condition smells like heavy exhaust.
When in neutral, the spark plugs we're just able to fire the lean mixture, when in drive the air passing the crack in the throttle plate is slowed since the engine drops in RPM, and when there was JUST enough pull on the fuel holes in neutral, there was NOT enough pull on the holes in drive so the engine just died, makes sense.
Here is how the idle circuit works. At idle, the engine is pulling air on the bottom of the carburetor. The primary throttle plates are barely cracked. Fuel is waiting at the little crack in the throttle plates in little round holes in the carburetor body. The little round holes are at the end of a idle tunnel which runs through the body of the carburetor and leads to the float bowl where the fuel sits. The idle screws are used to control the amount of fuel that flow through the idle tunnel, the screws intersect the idle tunnel. When you turn the screws out more fuel can flow, conversely when you screw the screws in, less fuel can flow. You have to follow the idle tunnel from the baseplate to the body of the carburetor and make sure it's free and clear with a air hose and a tiny air gun so you can hear the movement of air to the float bowl.
I just rebuilt a 1964 390 police interceptor 4100 and the thing had all sorts of problems from other incorrect repairs. It wasn't easy. The utube tutorials we're very helpful to me to sort it out. Now the car run runs awesome, I doubt a carburetor shop could have done the job right. It was not something that could be rushed. I had to stone several parts to flatten them out for proper sealing and to eliminate leaks, this alone took me a couple of hours. The diaphragm for the secondary venturi pull off that came in the kit was too thin and I was unable to get it to seal when I applied vacuum to it. So I purchased a good one for 25 dollars, the whole kit cost me 30 dollars! Remember these cars are 50 years old and one has to have a simple, but practical understanding of the carburetor to do the job right, and all carburetor parts are not created equal. Good luck!
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Whatever happened here? Did Angela get a different carb?
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Thanks for asking BossBill. What happened, you ask? I read every Ford/Holley 4150 book and article I could find and rebuilt the carb two more times. I adjusted everything possible, to the best of my understanding. The engine continued to run exactly the same, however.
Finally, a friend graciously allowed me to borrow a known-good 4150 off of his running Mustang. I set his carb onto my engine, changed nothing else and my car ran perfectly.
I ended up rebuilding another spare carb I had and used that one, which also worked perfectly on my engine.
So, in the end, I was defeated (through no lack of effort) in that the carb won.... I could not for the life of me determine what was wrong with it. Even the famous Joe Bunetic carb rebuild rendered the same result. Sorry guys, I tried... Thanks for all of your help!
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Angela,
Id suggest Drew Pojedinec at AirFuelSpark if you are still looking to get that carb working. It could be any number of things, often even new components are incorrectly machined. I had a BOSS carb that Joe did for me several years ago and I could never get it to run well, even though it looked fantastic. I sent it to Drew, who went through it and blueprinted/re-checked everything, found a couple issues. It runs great now.
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Her carb has mixture screws in the baseplate as well as metering block.
It was running lean the whole time. Sometimes those baseplate screws reduce fuel too much.
When you put an engine in gear it swings lean.
This stalled the engine.
This is why you set mixture at idle in gear with an auto. With a manual you set no load and richen a bit from there 1/4 turn maybe.
My advice would have been to turn the mixture 2.5 turns out from seated and go from there. Turn in 1/4 turn and test. Turn 1/4 and test.
There is also the possibility that the ifr had some trash in it.
390GT carbs are more irritating than most, her issues are common. Moreso when people install aftermarket camshafts.