Hope I have better luck with this first post than I am having with my first engine rebuild.
I have a newly rebuilt 1957 235 that has a tip-in stumble so bad the engine will stop if I don't quickly back off the throttle after a hard acceleration. I see other posts with the problem but so far I haven't seen any solutions that have worked.
The engine is running on a test stand right now. I installed Fenton headers and the Fenton dual carb intake manifold with 2 B model, manual choke Rochesters. Carbs are rebuilt with no tags so probably have mixed parts installed. I am heating the intake manifold using the connection on the Fenton headers.
Accelerator pumps are throwing out good streams. I'm not sure that can be improved. Carb jets were reduced from 58s to 57s and a Colortune shows good blue flame throughout the range except when the throttle is blipped hard and then the Colortune goes to orange(rich).
Manually squirting raw fuel into the carbs on acceleration cures the stumble so it seems I am starving the carbs although the Colortune seems to indicate otherwise. Vacuum drops to zero when throttle is hit so how can carb get gas from any port if there is no vacuum for a split second? If this is the problem, what's the cure? Vacuum is steady 17 at idle.
I have a Mallory dual point dizzy and a Pertronix coil. Points, plugs, valves have been checked and rechecked--per the appropriate specs.
Any help would be greatly appreciated. I can't install the engine running as it is and this project is rapidly turning from a therapeutic exercise into a major stress inducer.
Thanx to all.
