SBC stumbles/dies under load - Enigma, ready to torch it! - Page 3 - Hot Rod Forum : Hotrodders Bulletin Board
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Old 02-01-2012, 04:11 PM
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Originally Posted by highgrade
Enigma solved! Almost.

I FINALLY figured the cause of my stalling under load. After doing a test run with a fuel line sucking from a well vented portable gas tank and bypassing all the EVAP and vent line stuff, it ran fine. So, my problem was related to too much vaccum in the tank, pulling against the mech. fuel pump. I tested both gas caps (main and aux. ) tanks and although they are vented (in), it was not alot of venting. I went to NAPA and found another cap, that had alot less restriction, which I think will ultimately solve it. I think my strong vacuum was more than the cap could vent, and after a load was placed on the engine, it developed a strong vacuum in the tank that the pump could not work against. I could have sworn I tried driving without a cap during my months of diagnosis, but must not have had the right combination.

So my final question is which vacuum port on the quadrajet should be hooked to the carbon canister? My canister only has two ports (one to the tank, and one to the carb). Should the carb end be ported, full maniford, vac. switch, etc?

Thanks again.
Happy to hear you hunted this down, for as often as this happens, it skipped me.

Probably when you tested without a cap it was too much of a vacuum leak so it traded leaning out causes from an inability to pump enough fuel, to too much air for the fuel. Weird but plausible.

Bogie

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