vacuum advance issues

[fleetsidelarry]

Erratic, when the guys mentioned "stock" previously they were referring to a specific set of weight/plate, from a particular vehicle

Originally Posted by crazy longhorn

Dave, was the ign guru, that new the numbers on the weights....but basically, he said pull em ..from a 3/4 ton truck, what you will get, is a far better curve, than you will see on a car dizzy. Me & that old man butted heads pretty hard......but he knew his ****!

FWIW, I finally found my reference to Dave's weight/scroll plate #'s:
"Use from a Suburban, weights marked 41, center scroll marked 375."
and:
"..the 41/375 will give you another 22 crankshaft curve degrees.."
(ChevyTalk post #1449439 - 02/16/06 05:55 AM)

you can use a good aftermarket kit like MSD or Crane to get close to those specs. you can also find those weights and scroll plate on e-bay sometimes

[64stpside]

Brother, I JUST went though the same thing you are experiencing. I have a stk 305 and a rebuilt q. jet 4 barrel carb. I bought a skip white racing distributor with adjustable advance. I never touched the vac advance canister adjustment as I don't have the tools to dial in total timing yet.

Here's what I did to make it quit all the missing, backfiring and black smoke:

1. manifold vac is a must because lean mixtures need more advance to burn correctly, ported vac does nothing to the vac advance canister until you hit the gas and it sucks when you do hit it. Also it gets your throttle plate in the proper position for the transition point in the carb when you set your idle. The port must be sucking air at idle to be a manifold vacuum port.

2. My initial timing is at 8 deg....for now. Cars without an egr don't like a lot of initial advance as there isn't enough air being pumped into the cylinders to cool the charge and causes detonation. You can drive it a little at a time and keep bumping the initial up until you get detonation then back it off, which is what I'm gonna do.

3. Set the idle mixture screws with a vacuum gauge (look on youtube)

Hope this helps

[storm9c1]

Excellent summary of everything we've been suggesting on multiple threads.

[64stpside]

Originally Posted by storm9c1

Excellent summary of everything we've been suggesting on multiple threads.

Thanks. You guys have been great with all the advice. I know the frustration that others are going through and it feels great to get things right

[crazy longhorn]

Erratic....Moroso, Mr gasket, MSD, ect aftermarket weights are very lite weight, & have very lite springs to work with them. Try what you have, see how it works (been there done that)! the problem with the mix , is that to get the proper curve, you are usually to loose at idle speed...(in other words, the ign is advancing@ or below idle speed. You do not want this....as Larry stated, the advance should not start before 850 rpms,& it should end @ 3000 rpms (2800-3200). I found a better street curve , using good stock weights/plate, from the 3/4 to 1 ton trucks, with the Crane kit that I listed part # farther up the page. I wish you the best....let us know how it goes longhorn

[gvw5400]

Gentlemen,
I would like to personally thank all of you guys who offered great advice to Erratic!
I'm sure most of you learned timing issues like I did, MUCH trial and error.
This site is great and helpful, all thanks to folks like you!
Thanks again.
All the best, Dirk