Technical Help: truck will only idle with constant foot on the gas

Hey guys,
I’ve been working on my 1957 gmc pickup project and I’m just trying to work out the kinks. I can’t seem to get the truck running smooth. in order for me to keep it running or sitting in idle, I need to keep a constant foot slightly on the gas pedal. As soon as I fully disengage the pedal, it sputters and dies. I got the carb rebuilt, replaced the: fuel filter, spark plugs, condenser&points. All in hopes of fixing this issue but nothing!
Is there Anything else that I’m missing and can try?





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What kind of carb is it? Should be able to just turn the idle up

 

Idle mixture not set right? Turn the mixture screw right in until it stops, turn out about 1 & 1/2 turns.

 

vacuum leak.
6 cylinder or v8?

 

It’s a V6 (235). How do i verify if it is a vacuum leak?


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Is the choke fully open after the engine warms up a bit?

Is the idle speed screw backed out too far?

How much initial timing are you set at?

Have you got a vacuum leak, vacuum hose not connected somewhere, a vacuum hose damaged somewhere that's not easily seen?

If you can get it to idle at all do you see fuel dripping from the main nozzles or vent tube when you look down the throat of the carburetor?

Did you check the distributor shaft for excessive side play? If it's a points type distributor, what's your dwell or points gap?

 

listen for a hissing sound.
plug off all vacuum fittings.
lightly spray carb cleaner along all the intake gasket areas and listen for the idle to increase. [it will suck in the fluid through the leak]

 

If it has a manual choke does pulling the choke knob out make it better or worse?....if it runs ok down the road and is just an idle issue pulling out the choke helping means your too lean( vacu leak, idle mixture screws not out far enough, float level too low) if the choke makes it worse your too rich ( idle mixture screws too far out, leaking power valve, float level too high....if the choke out some helps and it acts like you need to constantly pump the gas pedal to keep it running you may be trying to use ethanol blend fuel and need to go to larger main jets.....better describe your symptoms for a better diagnosis!...good luck and get back to us!

 

So I found the issue... after trying just about everything, I walked went through my firing order and instead of 1-5-3-6-2-4 I had 1-5-6-3-2-4! I’m surprised I was able to drive it like that for who knows how long. Thanks for all the help regardless!


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