I'm working on my brothers truck, a 80 chevy with a 454 that he just put a eldelbrock performer plus cam/manifold package, headers and a valve job.

Ever since he did everything it had developed a miss and runs really rough and has no low end power.

I just did a tuneup with new cap/rotor, plugs and wires but it still has a bad miss and sometimes pops out of the exhaust when you rev it. Tried rebuilding the carb(q-jet) but it didn't help either. It's running very rich as the plugs were dark and a little wet looking, and you can just smell how rich it is by the exhaust smell. Went to adjust the idle mixture screws but they did nothing at all, was able to screw 'em all the way in and it still ran

Did a compression check and got these numbers:
#1-135lbs
#2-135lbs
#3-140lbs
#4-145lbs
#5-140lbs
#6-125lbs
#7-135lbs
#8-125lbs

I see a couple cylinders are low but it should run better than it is.

Any suggestions on what I can try next?
Of course I wanted to try a different carb but since all my vehicles are injected I sold all my holleys and q-jets

 

compresson is fine. try running the valves, setting timing, checking for vacuum leaks

 

Already checked that stuff, still no good

 

cam timing would be my next guess if you're sure all the tune up parts and settings are good

 

Well, the cam was installed straight up recently with a new double roller set so I'm positive that's not my problem.

Boy, this is driving my nuts

Guess I'm gonna pull the carb and go through it, since it's not right either. Maybe it's flooding the engine out

 

Maybe the distributor is off 180* or so. Maybe you got a couple plug wires crossed? check that the valves are adjusted properly.

 

Just to add to what was already said, maybe your choke stuck open/closed?

 

I think I have narrowed it down to a bad carb, went through everything and readjusted everything and went through the carb again and it only misses now when it idles for a while, like it's loading up with fuel, then if I rev it for a few seconds it clears up. Carb's been rebuilt twice so it must be a internal leak in it somewhere.

Gonna try and find a carb I can use to try on it before I buy one.

Thanks for the suggestions.