Hello, I am new to this forum and I have a concern. I recently purchased a 383 crate motor. I have put about 250 miles on it since I purchased it. I have been chasing a problem since I dropped it in my car. My total timing is set to around 36 degrees. I am using a demon 750 vac. sec. carb. If I plug both ports on the carb and plug the vac. advance canister on the dizzy, the car runs fine. If I hook up the vacuum advance to either ported or manifold vacumm, the car acts like it is missing real bad at cruising speed. I am assuming that means it is getting too much timing. What can I do to fix this? Since the car seems to run fine without vacuum advance, can I just leave all ports plugged?

Heres what I know about the motor
Approx. 500 lift roller cam
Pro Comp 190 heads
dual plane aluminum intake
demon 750 vac. sec. carb
roller rockers
Scat bottom end
Full length headers
3 inch flowmasters
Electric fuel pump

Any advise or help would be appreciated.

Is your vacume advance ajustable?Would use an alen wrench through the vacume port if was.

Check to see if the vaccum advance is leaking. Use a hand held vaccum pump to test. sounds like it may be leaking.

It would seem to me that if it wee leaking you would be getting less adavance out of it due to less movement in the slot?

Sounds like either your advance canister is providing more advance than the enigne can use or your total is higher than you think. Are you sure that all of the mechanical was in where you checked total?

Sounds like either your advance canister is providing more advance than the enigne can use or your total is higher than you think. Are you sure that all of the mechanical was in where you checked total?

X2!

If your total is correct I would start limiting the vacuum can 2 degrees at a time till it runs clean. An adjustable vacuum can will only help the pull in and all in timing (of the vacuum can itself), not the overall amount it adds.

What distributor?