Just rebuilt my Rochester B carb on my 1956 Chevy 235 and bolted it back up. Fired up the engine and let it run for about 15 minutes at idle and it was running real great. Then I gave it some gas a few times. The third time I gave it gas slowly and evenly there was a loud "POP" that came from the engine bay when I applied the throttle. I figured it was just the carb needing tuning so I went to turn the idle screw after which I grabbed the throttle linkage and revved the engine again and this time the "pop" came right up through the top of the carb. My question is what could be causing this backfire through the carb? Could it be a timing issue, or could it be something wrong with the carb after it was rebuilt? The car ran just fine before the carb was rebuilt due to a leaky gasket causing the engine to sputter and die with quick acceleration. Also, It only backfires under throttle, and not during idle. Thanks in advance...
It must have something to do with the carb if that was all you changed. Popping back through the carb is usually caused by a lean condition. That can be caused by low float level, bad accelerator pump or power valve or a large vacuum leak.
I would check the accelerator pump. Is it spraying a good stream? Also, is it spraying at the right time? It needs to be adjusted to spray correctly. Good luck
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