QuestionI have a 1985 GMC Stepside with a 4.3 liter and a stock manual trans. The engine is a rebuild from Jasper and a Carter carb 3 years ago. I'm not sure of the type of choke. It backfires on some upshifts and some decelerations, but usually on the release of the accelerator. I have replaced the muffler and now I have to replace the Catalytic Conv (hole). A friend mentioned posiibly adjusting the carb (What do you think and if so, How?)
AnswerI do not know what model Carter carburetor you have, but it may or may not be adjustable. The idle mixture screws were sealed at the factory and can be removed, with difficulty, to allow adjustment.
If you see screws with springs behind their heads near the base of the carb, on the front side of it and centered in each barrel, those are the adjustment screws. If you see two shiny steel caps, the screws are sealed and recessed behind the caps.
Adjustment is usually fully closed, then backed out two turns. With the engine hot, turn each screw in 1/4 turn or less increments (turn each screw equally) until the best idle is obtained.
You might also have a stretched timing chain if the engine has a lot of miles on it.
Also, check for an intake leak. Spray carb cleaner along the intake manifold where it meets the cylinder head. Any change in engine speed indicates an intake gasket leak.
