23 in. of vacuum is a bunch! certainly no vacuum leak. does adjusting the idle screws affect the idle? if not, look for an idle circuit obstruction (dirt). are the throttle butterflies nearly closed at idle- if the throttle is open too much at idle you could be losing the function of the idle and off-idle circuit. How is the vacuum advance hooked up, manifold vacuum or to some point above butterflies? Maybe due to a backfire the power valve diaphram is busted (naah-excellent manifold vacuum), actually I've never seen that high of vacuum readings at idle with any cam, all my stock experiances have been under 20 inches. Not to into Holleys but just some thoughts-does it pop back thru the carb- or just stumble?
Oops, you said it do respond to idle screws, It seems to my old school pre-smog experiance that 14:1 is pretty lean for an crude idle circuit. This was something considered a bit lean even at cruise conditions in the 50's/early 60's. Try riching up the idle to say somewhere in themid to lower 13's and see if it helps. Lean idle mixtures required 195 degree thermostats, reduced timing, heated air to the AIRHORN. Look at your stock air cleaner/ exhaust manifold, it had a "stove" providing hot air to the carb because those carbs were jetted so lean from the factory. You cant expect an aftermarket carb to perform as well as the original setup did from death valley to pikes peak and mountain iron to Arizona - the original was custombuilt by the factory to handle all the above situations and every thing in between. The only gripe is that it was too small for the hotrodder. Everything is a compromise. And then came smog controls- in 1974 chevrolet even "loosened" the torque converters to help their "stumble" problems. I think richen up the ilde.
Last edited by preacher-no choir; 12/12/1104:22 AM.
