school me on gassers...

[colbystephens]

ok, so I got this c20 w/ a 454. if you stomp on the gas, it stalls. you can only ease into it to get it to move - ease is not light enough of a word. i mean barely get on the gas at all. the problem happens no matter what speed you're going: off idle or cruising.

the truck has likely not had a tune up in 15 years. does the carb just need to be set up? talk to me like i know nothing about carbs or gas engines - 'cuz i don't. pics to describe what you're talking about are helpful.

'83 c20, 454.

 

[ryoken]

I'm assuming it has a quadrabog on it...

check that the accelerator pump is working... it's the cylindrical rod (about 1/4" diameter) that sticks out the top in the front.. it's actuated by a lever.. just push it down and watch the primaries to see if its dumping fuel...

 

[76zimmer]

yep that would be a good start...just take off the air cleaner and open the choke plate in the front of the carb by placing a large screwdriver on the front of the plate (front of vehicle) the plate should open easily. Look down the throat of the carb. If you move the accelerator linkage even a 1/4 inch you should see a squirt of fuel shoot into the openings in the carb venturis. If that works, check the choke mechanism operation. If cold, the plate should be fully closed, and slowly, but fully open up within a couple minutes after the engine is running. Don't worry about the big plate in the back of the carb for now. That is the secondary side of the carb.
Does the engine run reasonably stable at idle?

 

[colbystephens]

yes, it idles fine, and runs up the rpms fine too - just not too quickly.

 

[Wrench]

First thing is use some carb cleaner and make sure everything's moving easily and the way it's supposed to.

To test the accelerator pump, disconnect it (vertical rod at front driver's side corner of the carb with a lever arm on top of it) by tapping in the pin that holds the lever arm. Then see if the bog is worse or better. If it improves, then you have a rich condition, if it gets worse you have a lean condition. If nothing changes the acc. pump isn't functioning.

 

[LOGANSTANFORTH]

i love the quadrajet on my truck, better than any holley or edelbrock....


it probably wouldnt hurt to just take it to a good carb shop (very few exist anymore) and have it rebuilt.....a good tuned QJ is one of the best carbs ever built.....

 

[75GmcJimmy4x4]

another area you may want to check is the fuel pump and the fuel filter the filter may be clogged and not allowing the fuel pressure to build up so you have the reserve pressure available when you mash on it ..... thats what happend to me on my 75 with a 350 and a holley t/a

 

[El Larry]

How old is the gas in the tank, also if it sat for years, it needs to be completely drained, or whatever bad gas was left will make any new gas bad as well.

 

[El Larry]

Also there is a small screen filter on the carb where the fuel line bolts onto the carb, if I remember right, you have to unscrew it?

 

[dyeager535]

Have you checked the timing? I've seen some massive differences with timing changes.

Other thing is a normal tune up. Plugs, wires, cap/rotor (cap/rotor only if the ones on it are bad, which is a visual inspection) and a good visual inspection of the engine bay, especially looking for broken vacuum lines.

 

[dyeager535]

Stock quadrajet filters will bypass if they are plugged, so theoretically should never cause a problem with the way a vehicle runs, at least until it bypasses crud into the float bowl.

 

[colbystephens]

thanks for all the ideas on things to check, guys. the truck is 200 miles north of me - i was going to pick it up this week but had some family crises to deal with. so, this project is on hold.

the gas in the truck is not old - it gets new gas each time it needs to be used and the tanks are basically kept empty simply because there's no reason to make the fuel tank a savings account...