Explaining Ignition vaccum canister
Thread Starter
Le Mans Master
Joined: Mar 2001
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From: Lincoln, CA
Explaining Ignition vaccum canister
My L36 has always bucked just off idle with makes parking lots a wonder experience.
With the change to a 496, different roller cam and a QFT 830 it still bucks.
I had it on the Dyno and the operator noted that my timing was jumping all over the place at idle.
So after much reading it sounds like I can try different Vacuum Advance cans that operate at different Hg.
My car idles at 14Hg. Some of the suggestions are the VC-1810.
What I don't understand is how to select a can that can deal with the bouncy 14Hg at idle.
The VC-1810 states Application Starts @ “Hg Max Adv (Distr. Degrees @ “Hg.)
3-5 8 @ 5.75-8
So if I'm reading the above correctly the 1810 will kick in at 3/5 Hg and add 5.75 to 8 total? That sounds horrible.
With the change to a 496, different roller cam and a QFT 830 it still bucks.
I had it on the Dyno and the operator noted that my timing was jumping all over the place at idle.
So after much reading it sounds like I can try different Vacuum Advance cans that operate at different Hg.
My car idles at 14Hg. Some of the suggestions are the VC-1810.
What I don't understand is how to select a can that can deal with the bouncy 14Hg at idle.
The VC-1810 states Application Starts @ “Hg Max Adv (Distr. Degrees @ “Hg.)
3-5 8 @ 5.75-8
So if I'm reading the above correctly the 1810 will kick in at 3/5 Hg and add 5.75 to 8 total? That sounds horrible.
Le Mans Master
Joined: Oct 2006
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
I had an issue with a 421 SBC once-- the mechanical advance springs were right on the edge of letting the weights move. Timing was all over the map. Swapped to a little more spring and it settled right down. Still had a good curve too. Might be worth a shot in your case too.
Thread Starter
Le Mans Master
Joined: Mar 2001
Posts: 5,738
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From: Lincoln, CA
Team Owner
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From: Western NY
Race Director
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did you disconnect the vacuum advance and plug the line and drive it to see if the problem went away?
not sure how you transcribed those numbers but I found for the VC-1810
0 degrees of advance at 4" of vacuum
16 degrees of advance at 8" of vacuum
not sure how you transcribed those numbers but I found for the VC-1810
0 degrees of advance at 4" of vacuum
16 degrees of advance at 8" of vacuum
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Safety Car
Joined: Apr 2006
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From: BC
The VC1810 starts working at 3 to 5"hg and produces a max of 16 degrees advance (that's 8 distributor degrees) at 5.75 to 8"hg. I believe you should have a can that produces max advance a minimum of 2"hg below your idle vacuum for proper operation and decide how much advance you need.
Last edited by CanadaGrant; Jul 14, 2017 at 10:48 PM.
Drifting
Joined: Feb 2005
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From: Los Gatos CA
Dan - My iron headed, high compression 60's motors (the L36 and '65 4-4-2) will buck like crazy at low-load with any more than 10* vacuum lead. Less is better. Of course our CA wannabe 92 "Premium" doesn't help things.
Safety Car
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From: BC
Last edited by CanadaGrant; Jul 15, 2017 at 12:03 AM.
Had a 1976 L-82, 4-sp
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From: Some days your the dog and some days your the hydrant.
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Just to add, my 355 didn't like 16* initial and hated 12*. It does like 22* initial and runs very well along with 12* mech'l and 8* vacuum advance.
