I have a 53 Belair with a '54 235. I was out cruising today and a few times it started stumbling and acting like the carb was loading up(as if I had pulled the choke all the way out). I would be cruising along a steady 30-40mph and all the sudden it would start stumbling for 30-60 seconds and then go away all on its own. Didn't seem to matter if I tried to accelerate out of it or hold the throttle steady. It did seem to only do it under load, because if I pushed in the clutch and just coasted, it would idle fine. I don't think it's a fuel problem because the tank has been flushed, all lines are new, filter is new, and carb was rebuilt not long ago. I was thinking more like an advance problem, just not sure if it might be a vacuum issue or maybe the mechanical advance weights are sticking. The distributor does move when I rev the engine and it idles and accelerates fine. It happened 4-5 times today, but never died. Any suggestions on how to verify if it would be a vacuum or mechanical advance issue or anything else to look for would greatly be appreciated. Thanks!
Normally under load like that it's a fuel delivery issue. Not enough fuel flow. Dirty filter...possible crack in the rear rubber line to the sending unit..etc. if you're confident it's not fuel it could be too much timing. Too much advance will cause a bucking like that under load too... maybe a spring is broken on your mechanical advance. Lastly I don't remember if you mentioned your ignition...but if you have points.. swap them out...put in a new condenser..sometimes they give funny symptoms like that. Could also be a spark plug or spark plug wire going out...those show up under load. There is a saying....that most carb issues are ignition related ...doesn't sound like an expensive fix though..
Clean the carb. Then burn good gas in the car. Corn gas generates it's own trash in your fuel system ...
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