Restoring - General discussions that span across many different groups of years and models > Drivetrain
Vacuum advance bad / 289 2 barrell ??
tobkob:
When you disconnect the vacuum line I assume you are plugging the end to prevent a vacuum leak. ;)
TOB
67350#1242:
It is pretty easy to check the vacuum advance diaphragm by applying vacuum. You can also watch the movement of the breaker plate if you remove dist. cap while applying vacuum. Attaching a hose and sucking on it should be sufficient if vacuum pump not available.
As far as I know, no vacuum advance is in play at idle if the vacuum source is at the vacuum port of the carb. Vacuum only appears there off idle.
tobkob:
--- Quote ---The miss is at idle but also when i hit the "spot" between getting off the gas and stepping on the gas,
--- End quote ---
I was asking just as a gentle reminder. ;)
TOB
jwc66k:
--- Quote from: 67350#1242 on October 19, 2016, 10:31:45 AM ---It is pretty easy to check the vacuum advance diaphragm by applying vacuum. You can also watch the movement of the breaker plate if you remove dist. cap while applying vacuum. Attaching a hose and sucking on it should be sufficient if vacuum pump not available.
As far as I know, no vacuum advance is in play at idle if the vacuum source is at the vacuum port of the carb. Vacuum only appears there off idle.
--- End quote ---
If you don't have a vacuum pump you can still check to see if the diaphragm is functioning with it still mounted on the distributor. With the cap off and rotor removed, remove the tube (metal or rubber) from the port to the carburetor, and disconnect the diaphragm arm inside the distributor. Put your finger over the port and move the arm outward. You should have a small amount of pressure at the port. With the arm outward, put a finger over the port and pull the arm inward. You should have some suction indicated by the arm wanting to go back outward. It's a quick test. If no pressure or suction, bad diaphragm. This test does not indicate if any of the internal washer spacers or the stop are correct.
Jim
Hipo giddyup:
Good pick up on the vaccum advance not being used at idle, but i believe I was giving it gas when i noticed the miss disappeared. :o Its been a week since i was playing with this and have been quite busy to get back to tinkering. I do have a vacuum pump and will test that.
It sounds like this car should have a steel line as factory original so i have an NOS line I will be installing tongiht and will perform the test at that point. If the diapram is good, the steel line replacing the rubber hose (to rule out a crack or other issue), then what part of the carb could be creating the miss? Perhaps a pasage is fouled or blocked?? The car was fully restored in 2000 and since then, only has about 3,000 miles on it. Alot of time idling in and out of the garage when I couldn't take it out for a spin, such as during winter, so maybe there is carbon build up? just guessing at this point. I can always do a quick carb rebuild with a new kit. That's easy and cheap enough.
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