I'm assuming that you're running a Rochester 'B' stock carb is that correct p.j.?
Did you have that problem before you rebuilt the engine?
This symptom has been hashed over hundreds of times and I have yet to find anyone that has an answer to it. I've run into it myself and after a couple of years and a half dozen 'B's finally threw in the towel and solved it with a Carter W-1. I've talked with dozens and dozens of people who are well versed in automobile theory and excellent wrench twisters, that have run the 'B, and I keep hearing the same story over and over. That is the “they can’t get the stumble out of it” and then there is always, “just ignore the factory specs and jack the timing up till it pings or won‘t start any more.”
I disagree with the timing issue and believe that these engines when stock and in good mechanical condition should run just fine with the stock settings. You don’t get much more basic than these Stovebolt engines and the ignition system is pretty simple to set correctly. One thing that I would say about the distributor is that during a rebuild all to often guys simply wash, paint and put in a new set of points, condenser, cap and rotor then call it rebuilt. They don’t completely disassemble and service what’s under the breaker plate. As with the carburetor a careful complete disassembly, cleaning, lubrication of the weights and check of the springs is necessary for it to for it to operate the way it was meant to. And don’t forget to check out the Vacuum diaphragm for proper operation.
With that said, what’s my solution? Like all of the experts, I of course not being one of them, simply don’t have a logical concrete answer. About all I can suggest is what you have already done, CAREFULLY and THUROUGHLY rebuild your ’B’, make sure your float level is right and the check balls are in where they belong . Make sure that the high speed circuit is working correctly paying special attention that the power piston is free and that the plunger is not bent or binding at the main well and that it works VERY smoothly and that the spring is correct. Because this is a vacuum operated device that operates with a very small vacuum signal and is probably the weakest link in this carburetors chain of events.
I had a theory that the fuel was the problem because it was diluted with alcohol. Alcohol as a fuel does not have the same energy that gasoline does so you need to burn about 1/3 more to get the same performance from an engine burning straight alcohol. I’ve experimented with avgas, non-alcoholic racing fuels, I’ve even driven out of state and brought back five gallons of regular auto fuel that did not contain alcohol and none of this changed the way the engine ran with the ’B’ carburetors on it. Switch to the W-1 and problem gone.
So I guess some will ask, “why did that jerk bother posting this reply if he doesn’t have an answer”?
Well, cus I suppose that ’m just trying to give ya some moral support p.j. and let you know that it might not be you or your tuning skills that are at fault, it just might be that you’re dealing with a carburetion device that was a poor design from the get go.
Denny Graham
Sandwich, IL
