83 z28, rebuilt 305 bored .30 over.holley 600 vacuum secondaries. msd streetfire distributor. edelbrock performer intake. Timing set to 36*. swapped in medium springs in distributor. thumper 279H cam. only about 500 miles on rebuilt motor.

Motor won't idle in gear(idle mixture screws set to 1.5 turns out) won't accelerate hard down low. Changed accelerator pump nozzle to a 35, up from the stock 31. Power valve changed to a 2.5, also have tried 4.5 and 6.5 none seem to change anything. Changed accelerator pump cam, hesitation a bit better but far from being good. Surges throughout rpm range,just gives the car a slight bump. Haven't touched the jets yet. Still has a lot of blowby. Little smoke from exhaust, a lot out of breather on valve cover. Seems to pull ok once past about 2000 rpm except for surging, and chrips second gear pretty well. Any suggestions?

 

What do you have for exhaust?

What valve springs did you use? You did see footnote 7, right?

I sure hope that 36 degrees timing is total mechanical advance.

You do realize the whole idea behind the Thumpr cam series is to produce an engine that sounds mean, won't idle, has no low-end power, and who cares about real power? They assume a 350 CID for the powerband and characteristics they state in the cam information - a 305 will only move the powerband up and make everything else worse.

 

I have hedman headers into a hedman ypipe which goes to a edelbrock sdt exhaust.

I changed the valve springs out with the cam swap along with the lifters. I took it to a local speed shop to check it out. they said the valve were set correct after the rebuild and the timing was as much as they could put in without causing it to be too hard to start. They said that sometimes a rebuilt motor just needs some miles on it to break it in. Is that correct?

I do know that the thumper is just for sound and probably need to get a 2000 stall convertor to make it move better on the low end.

And when you say won't idle, you mean in gear right? Before the rebuild the cam seemed to idle ok. Just didn't have power on the low end because i dont have a stall convertor.

 

Any suggestions on the surging?

I can deal with the hesitation till i get a higher stall convertor and can deal with it not idling in gear. I just would like to fix the surging and the blowby.