Anybody remember carburetors?

70 Blazer, 350, 300hp crate motor, have replaced fuel pump, installed hei ignition, 4bbl Rochester carb has been rebuilt.
I've got an occasional "loading up" at lower rpm's, 2000 or below. Engine
will die at idle. This has been occurring before and after a new engine and later elect. ign. Anyone know what might cause this Rochester 4bbl to do this? OR, could it be a non vented gas cap causing a pressure build-up to blow through the fp and past the main jets? I frequently have a pressure build up when I remove the cap to refuel (which is not too often with a 37gal tank). LD
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Do you mean it's too rich and floods out at times?
This has been occurring before and after a new engine and

The needle seat, needles, floats, etc in those commonly stick for one thing. Kind of sounds like the float or needle is sticking and flooding out maybe. Do you see gas dribble from the carb, or smell a strong gas odor when this happens?
OR, could it be a non vented gas cap causing a pressure build-up to

I kinda doubt it. Usually in a case like that, the tank collapses, and you starve for fuel, rather than have too much pressure. I'd make sure the cap is correct for the truck, but usually having some pressure is normal. MK
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When carb was rebuilt was the float replaced. The floats have been known to become saturated and less buoyant causing flooding at idle or low load.
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