Quadrajet spitting/popping/missing

[78GMCJIMMY]

My 1978 GMC Jimmy w/ a 350/t-350/np-203 Has developed a miss.It has a slight miss at idle when warmed up,and when accelerating it stumbles/pops/misses or coughs back through the carb. The carb is a remanufactured quadrajet Which is about 4 years old and has about 30000 miles on it. The motor was rebuilt 2 years ago.I have checked for vacuum leaks and can find none. However the carb seems to have a louder than normal hiss?Help WTF Is wrong? I sospect the carb is shot or ? Any help is greatly appreciated!Could the power valve be blown. I guess it's time for a Jiffy carb kit ay.

 

[78GMCJIMMY]

Anybody Home!!!!!!!

 

[pauly383]

Did you spray the carb at the thottle shafts ? It doesn't sound old enough to do it ,but who knows who rebuilt it .

I do know thta weather can effect the way it runs , as well as altitude .

 

[chopped&bobbed77burb]

I bet your accelerator pump is shot and you may have also missed a damaged vaccum line as they can crack or split . Also check the 2 air screws and make sure they are adjusted properly . Just by a rebuild kit , float and a new fuel filter . I have alway's ran q jets on my chevy's and they have alway's done me right . 4 year old carb with 30k on it should need a rebuild . hope all goes well and good luck .

 

[78GMCJIMMY]

I Found the Problem

Well here is an update. I rebuilt The quadrajet on friday night and saturday morning I took her out for a test drive. Ran bitchin' then POP and WTF. : So I figured it must be the ignition and swapped in an old plug wire set. While doing this I found the problem was a loose vacuum fitting where the vacuum modulator for the t-350 hooks up on the intake manifold! ! 1 and 1/2 turns and whoala fixed! IDIOT GEEZ!! Anyhow the carb needed the rebuild anyway it was pretty f*****g dirty and gunked up! now the jimmy is back in top form purring like a LIGER once again. Thanx for all the help!Have you ever taken that thing off any sweet jumps!

 

[chopped&bobbed77burb]

Well here is an update. I rebuilt The quadrajet on friday night and saturday morning I took her out for a test drive. Ran bitchin' then POP and WTF. : So I figured it must be the ignition and swapped in an old plug wire set. While doing this I found the problem was a loose vacuum fitting where the vacuum modulator for the t-350 hooks up on the intake manifold! ! 1 and 1/2 turns and whoala fixed! IDIOT GEEZ!! Anyhow the carb needed the rebuild anyway it was pretty f*****g dirty and gunked up! now the jimmy is back in top form purring like a LIGER once again. Thanx for all the help!Have you ever taken that thing off any sweet jumps!

Glad you got it fixed . Did you also have some shifting problems with that vaccum leak ?? sometimes the vaccum line can pop off the modulator at the tranny and cause the same carb problems and shifting issues . I run a can of Berrymans B-12 fuel system cleaner about every 3 months in all my rigs and it seems to help and the fuel filters seem to last abit longer . As for jumping the burb No! I have had the front end off the ground about 5 feet trying to bounce it up over some rocks . I only did it cause I have a dana 60 and I would have never done it with my d44 (snap) . my burb is pushing 7000lbs. Maybe I'll try it after I box the frame . see ya on the trail some time .