too much initial adv?
Thread Starter
Joined: Jun 2005
Posts: 1,245
Likes: 8
From: Fairfield, CA
Car: 91camaro rs,2014 silverado 5.3L
Engine: 5.7Lcarb,5.3L
Transmission: 700-r4, 6L80
Axle/Gears: strange 3.73's
too much initial adv?
well with the distributer advance removed and pluged i set it to 0*. then as soon as i plug the dizzy back in it goes up to about 16 to 20* with it just idleing. i thought it wasn't soppused to increase till you gave it gas? there is only one vacuum port on the front of the carb also so i know it has to go to that one. anyone have an opinions as to what could be wrong?
Joined: Mar 2000
Posts: 43,187
Likes: 42
From: Littleton, CO USA
Car: 82 Berlinetta/57 Bel Air
Engine: L92/LQ4 (both w/4" stroke)
Transmission: 4L80E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
With only 0 degrees initial advance, you're going to have to set the idle speed screw in so much that you will uncover the ported vacuum slot.
Set initial to 8-12 degrees advanced with the vacuum advance disconnected. Then reconnect the vacuum advance, set idle speed and mixture.
Set initial to 8-12 degrees advanced with the vacuum advance disconnected. Then reconnect the vacuum advance, set idle speed and mixture.
Supreme Member
Joined: Sep 1999
Posts: 7,072
Likes: 13
From: Philly, PA
Re: too much initial adv?
What distributor?
Many distributors give too much vacuum advance (frankly, almost all of them do). 10-12* max vacuum advance is all you need on a performance motor. That lets you dial up the initial advance for maximum WOT scoot (12-16* initial with vacuum advance disconnected being typical) without over-advancing at idle or encountering part throttle detonation.
If your vacuum advance is connected to a full manifold vacuum port (sounds like it is) then you'll pull in ALL the vacuum advance the canister is capable of supplying even at idle, unless you have a lumpy cam and don't pull much vacuum at idle (unlikely given your modest cam specs).
Don't be afraid of idle advance in the 25* range (with vacuum advance connected). That's perfectly OK with most motors. But if your vac advance can is giving 16-20* max then you're limited to an initial timing setting of only 5-9* to stay below that 25* point at idle, which is going to hurt your WOT power when the vacuum advance goes away (manifold vacuum drops close to zero). However, if you limit your max vacuum advance down to 10-12* you can run 13-15* initial timing without going over 25* at idle, which is going to work a lot better when you go wide open.
Many distributors give too much vacuum advance (frankly, almost all of them do). 10-12* max vacuum advance is all you need on a performance motor. That lets you dial up the initial advance for maximum WOT scoot (12-16* initial with vacuum advance disconnected being typical) without over-advancing at idle or encountering part throttle detonation.
If your vacuum advance is connected to a full manifold vacuum port (sounds like it is) then you'll pull in ALL the vacuum advance the canister is capable of supplying even at idle, unless you have a lumpy cam and don't pull much vacuum at idle (unlikely given your modest cam specs).
Don't be afraid of idle advance in the 25* range (with vacuum advance connected). That's perfectly OK with most motors. But if your vac advance can is giving 16-20* max then you're limited to an initial timing setting of only 5-9* to stay below that 25* point at idle, which is going to hurt your WOT power when the vacuum advance goes away (manifold vacuum drops close to zero). However, if you limit your max vacuum advance down to 10-12* you can run 13-15* initial timing without going over 25* at idle, which is going to work a lot better when you go wide open.
Last edited by Damon; Oct 1, 2007 at 08:26 PM.
Thread Starter
Joined: Jun 2005
Posts: 1,245
Likes: 8
From: Fairfield, CA
Car: 91camaro rs,2014 silverado 5.3L
Engine: 5.7Lcarb,5.3L
Transmission: 700-r4, 6L80
Axle/Gears: strange 3.73's
Re: too much initial adv?
i will move the initial up to 8 and go from there. thanks everybody for the quick help
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