timing question
Thread Starter
Instructor
Joined: Jan 2011
Posts: 221
Likes: 1
From: Sylmar CA
timing question
Just got my carb back today from Lars. I had also rebuilt my distributor, shimmed it, changed the capacitor, ignition module and magnetic pickup. Changed the cap, rotor and new vacuum advance can AR12. Reinstalled everything and hooked it all up. Fixed my timing to 12 degrees initial. Revved the engine up and total timing went up to only like 30-31 degrees. Hooked up the vacuum advance. Initial timing went up to 31 degrees and total timing is at 50 degrees. I know that being at total 50 with vacuum advance is good but is the total timing of 31 degrees without vacuum advance a problem? Something I was wondering today. And if it is any ideas on how I can fix it?
Intermediate
Joined: Feb 2012
Posts: 43
Likes: 0
From: Ocala FL
You have hooked up your vacuum to your distributor to engine vacuum vice ported vacuum. Find a ported vacuum port on the carb and hooked it up there. Look for a vacuum port that does not have vacuum below 1000 RPM. Good Luck Jerry
Race Director
Joined: May 2005
Posts: 10,674
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From: Millington Illinois
St. Jude Donor '08-'09
Perfect. You can have up to 53,54 total with vacumn so depending on your heads you want total timing between 32 and 35 with your setup. You need to increase your initial only to get this increase if lars dialed your carb in and run manifold vacumn. if no detonation your as good as it gets.
Last edited by 63mako; May 3, 2012 at 09:04 AM.
Tech Contributor
Joined: Aug 1999
Posts: 14,370
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From: At my Bar drinking and wrenching in Lafayette Colorado
Just got my carb back today from Lars. I had also rebuilt my distributor, shimmed it, changed the capacitor, ignition module and magnetic pickup. Changed the cap, rotor and new vacuum advance can AR12. Reinstalled everything and hooked it all up. Fixed my timing to 12 degrees initial. Revved the engine up and total timing went up to only like 30-31 degrees. Hooked up the vacuum advance. Initial timing went up to 31 degrees and total timing is at 50 degrees. I know that being at total 50 with vacuum advance is good but is the total timing of 31 degrees without vacuum advance a problem? Something I was wondering today. And if it is any ideas on how I can fix it?
Lars
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Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
The car will tell you if it's too much. If it doesn't like it, it will "jerk" or "trailer hitch" at light throttle cruise. If it doesn't, you're OK. But rather than limit your total timing, I'd fix or replace the vacuum advance and limit it to 12 degrees if i were you. Instructions are in my paper.
Lars
Lars
Le Mans Master
Joined: Mar 2008
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From: Oxford MA-----You just lost the game!!!!
You could install a vacuum can that only advances 16 degrees or so. I think Lars has a paper on vacuum advance that gives part numbers for vac adv cans that have different degrees of advance, shoot him an email and ask real nice, maybe he'll send you a copy. That's what I did, and I was able to get my timing to be 16/36/52.
Keep the shiny side up!
Scott
Keep the shiny side up!
Scott
Le Mans Master
Joined: Oct 2002
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From: Las Vegas - Just stop perpetuating myths please.
Try a vacuum gauge.
I have one on my '94 Z28 and use it all the time even with my electronic PCM controls.
cardo0
Le Mans Master
Joined: Mar 2008
Posts: 5,948
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From: Oxford MA-----You just lost the game!!!!
It reads like u are very interested in tuning. Maybe try a vacuum gauge that way u can see what manifold vacuum actually is while driving. Also helps u choose a correct vacuum can for the dizzy. That way u will see WOT vac goes to zero and find out what your cruise vac is.
I have one on my '94 Z28 and use it all the time even with my electronic PCM controls.
cardo0
I have one on my '94 Z28 and use it all the time even with my electronic PCM controls.
cardo0
Keep the shiny side up!
Scott
Drifting
Joined: Jul 2002
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From: The only Corvettes in Highett Victoria
[QUOTE=scottyp99;1580738626]Another nice thing about a vacuum gauge is that you can use it to get better gas mileage. Just try to keep the vacuum as high as you can while driving.
I had a vac gauge on a 1983 Holden six company car back then and by using it as scotty says, I got very good mileage out of it. In many ways, it's more use than a tacho.
Regards from Down Under.
aussiejohn
I had a vac gauge on a 1983 Holden six company car back then and by using it as scotty says, I got very good mileage out of it. In many ways, it's more use than a tacho.
Regards from Down Under.
aussiejohn
Thread Starter
Instructor
Joined: Jan 2011
Posts: 221
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From: Sylmar CA
Awesome thanks guys. I'll get on this today right after work. I should have the right papers for the dist vacuum cans. At first I was recommended vacuum can EV3818. But now it looks like ima have to return that one if my car jerks under light load. Hope all goes well. Off at one today pst. I'll get home and get on this. Thanks guys. I'll post what results I get.
Thread Starter
Instructor
Joined: Jan 2011
Posts: 221
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From: Sylmar CA
Bumped up total timing to 36 degrees without vacuum. With vacuum it seems to be at 52 degrees. Initial with vacuum is at 36". I haven't been able to try it because the driveway is full of visiting families cars. Will try tomorrow and post my results.
Le Mans Master
Joined: Mar 2008
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From: Oxford MA-----You just lost the game!!!!
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Keep the shiny side up!
Scott
Thread Starter
Instructor
Joined: Jan 2011
Posts: 221
Likes: 1
From: Sylmar CA
Tomorrow I'll try to check and see if I have any vacuum leaks. Still figuring out my headlights, might be the actuators. And for the idle screws, lars rebuilt and tuned my carb and now my car is running better than ever. So I don't really want to mess with anything on the carb. I really liked his work and how he gave me my carb.