Hi
My truck (318 2bbl auto) has a very strange stumbling problem
when it is cold. If I try to accelerate in the first 15 mins of driving,
it thumps and bangs and won't accelerate especcialy up hills.
The carb was just recently rebuilt but it did not do this before it was rebuilt.
I checked the choke and it works perfect. The heat riser is stuck open but it shouldn't cause problems this bad.
Any thoughts?

Thanks
Gerry

 

accelaration pump in the carb,or float level?? just a possible guess

 

my big question would be did you find the mixture screws on the bottom of the carb? i don't think it would be adjusted correctly if it was just rebuilt.

 

Yes, I did find them eventually. They were behind little plastic
plugs. Would you recommend just playing with them
or is there some sort of vacuum measure or something?

 

i think adjusting them may need to be done to get it running better. from what i have read it sounds like it is running rich which makes sense since it was rebuilt and the rebuild probably would have removed them to clean the carb. no a vacuum gauge is not required. most manuals recommend using a vacuum gauge or tach because when adjusting the screws you are looking to get the engine to idle as high as it can which would create more vacuum. turning the screws clockwise leans the mixture out and turning them counter clock wise to make it richer. you should adjust each screw about a 1/4 turn a at a time and adjust both screws equally. once you got it idling as high as you can then you adjust the throttle stop screw on the throttle leaver.

 

Hi
Today I adjusted the screws to the setting that gave the highest idle then i let it sit for several hours. Then I started it cold (-5 degrees), let it warm up and pulled out of the driveway and went to accelerate but it still stumbled and prevented me from speeding up.
Do you think the heat riser would cause symptoms this bad?

 

unless it is above 0 i think you will always a stumble when you first start driving it. my truck stumbles a bit when starting from a stop or when it shifts gears when it is below 0 for the first couple of km but after about 5 minutes of driving it disappears.

 

Mine is so bad it won't accelerate over 40 for at least 15 minutes and it did not do it before the carb was rebuilt. I can't wait till summer!

 

is that -5*F or C.

 

-5 C which is a warm day.