Need help I'm lost!

[76chevyc20454]

I have a 76 c20 454 th400 and when I cold start it it misses like no other. It spits and sputters around 400 but if I open choke it will smooth out and idle at 1000 until I hit the gas to kick off high idle. I'm stumped because if the choke is fully open it will run fine but if it's cold and the choke is closed it runs like crap. I've replaced spark plugs, cap, rotor, wires, ing coil. I don't think it's ignition, but what do u guys think? It ran fine and then I put a manual choke conversion on it because it kept high idleing and the choke wouldn't stay fully open and I took manual choke off and put the divorced choke back on and it's still the same?

 

[76chevyc20454]

Anybody? Please

 

[SlickGTP]

I'm no expert, but I'd wonder if the idle mixture is too rich...

 

[Georgeb]

Are you opening the choke at all once it starts? You will need it open a little or it will run stupid rich.

 

[rich weyand]

If it runs fine cold with the choke open the idle mixture is too rich, a common PO thing to do when he choke is broken rather than fix it. Warm the engine up, then lean out the idle mixture to highest rpm. Then try the cold start with the choke again.

The idle mixture could be way rich because the well plugs on the Qjet are leaking. Has the carb ever been rebuilt?

 

[76chevyc20454]

I rebuilt it myself, put new gaskets and float in it and cleaned it but it ran fine after I rebuilt it. I'll try what you said, it's running rich because it will backfire sometimes upon startup. And when the choke is engaged it will spit black smoke

 

[Georgeb]

I rebuilt it myself, put new gaskets and float in it and cleaned it but it ran fine after I rebuilt it. I'll try what you said, it's running rich because it will backfire sometimes upon startup. And when the choke is engaged it will spit black smoke

Check to be sure your choke is pulling open far enough on start up. A rule of thumb I use is about 1/4" 3/8" open

 

[76chevyc20454]

I don't have the choke pulloff hooked up because of the manual kit on it but I open it a lil when I first start it and it will run for about 10 sec an start to spit and sputter. If I open the choke slowly till I hit about 3/4 of the way open it will smooth out. I haved prob with the carb leaking gas out the side that's why I rebuilt it and the high idle prob was from the spacer I have on there. The linkage going from the intake to the carb wasn't long enough, so it kept pulling choke closed. I have a spacer on there because of the vapor lock prob I'm still having lol but I thought about taking it off. It was on there when I bought the truck

 

[Georgeb]

Well, you can take Rich's advice and adjust the idle jets with a vacuum guage and see if that helps

 

[highdesertrange]

to much choke for conditions. open the choke some. highdesertranger