28buick

I question for the engine people here. The motor runs great however during deceleration as I get below 1500 rpm I am getting bucking of the engine. Over time I have reduced this thru tuning but is this just the nature of the motor and gearing I have. Car is a 75 with 4 speed and 3:36 gears. Motor is a 383 w/ 10.5 comp. Older Barry Grant 750 vacuum Secondary on an Edelbrock rpm intake manifold. Older AFR 180 heads with full length headers. The cam is a Bullet hydraulic roller 230 @ .050 with 0.570 intake and 0.518 exhaust at a 109 CL. Intake was degreed to 103.

MelWff

How is your distributor setup,
what is total mechanical advance, initial timing, and what additional comes from vacuum?

7T1vette

This is with your foot OFF the accelerator???

28buick

18 degrees at idle 34 degrees at 3000 then 16 degrees of vacuum advance. HEI distributor

28buick

Yes this coasting with the foot off or very little throttle. Give it the gas and she goes.

lars

Try unplugging your vacuum advance and see if the issue stops. Your 16 degree vacuum advance is a bit long - you might need to limit it to no more than 12 degrees (if the problem goes away when you yank the hose off).

Lars

28buick

Thanks for the suggestion. Gonna pour tomorrow but Tuesday I'll take it out and try it.

Rescue Rogers

I bet your rpm is lower than that and its the gearing you have. What do you have for a 4 speed. M21 or M22. 3.36 and a M21 is a 7.392 final gear ratio. When you start from a dead stop what RPM to you have to get the motor to so it will pull smoothly. Even a 383 isnt going to pull like a 454.
And that cam at a low rpm is going to lope anyway. I had a similar one in my 327 and had to set my idle at 800 rpm to keep the engine and tranny happy