For some reason carb rebuilders have a hard problem getting 4300's to run right. At least from mine and just about everyone I know experience. If anyone has FIRST hand experience with someone who can rebuild a 4300 and make it run properly there are a lot of us out here that would like to know . Many say that they can but when you get the pretty restored carb it doesn't run right or runs ok for a week and then goes to s#!t. Many enthusiasts just give up trying to get one to run right and run a Holley.
Truth. They are a serious pain, I'm dealing with one now, can't say how many times I've had it apart now. One mod is to install a secondary needle block off plug which seems to help with common flooding issues. They are fairly simple carbs as far as the number of parts/pieces that get replaced during a rebuild. It seems they are quite sensitive to fuel pressure also.