Can/will anyone please elaborate on the use of a vaccume guage to set timing and set carb settings?   ALSO, what are the advantages/disadvantages of using regular, 87 or mid grade, 89 octane in our cars with moderate up grades.  THANKS 

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Check this out:

http://classicinlines.com/Vacuum.asp

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Mark,

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Warning: The surgeon general has declared that it is NOT unhealthy to smoke your competition AND I just discovered that my corvette is a hybred.  It burns gas and rubber! 

Any time you are using a vacuum gauge for tuning purposes, you want to make the adjustments to get the highest vacuum reading you can. Whether adjusting the carb, or the timing, you want the highest steady reading. And remember, every adjustment here will effect an adjustment there, so you have to go back/forth between adjustments until you see no more rise in the vac. reading.
Octane is what helps keep "ping", or detonation in check. The higher the octane, the less chance of ping, and the more timing you can run. The same engine, with the same tune, might ping really bad on regular 87 octane, but not at all on 93 octane, with no changes in timing. Running a lower octane in an engine designed/tuned for high octane requires timing changes, and possibly even sparkle-plug heat range changes. While there are no discernible power increase from running high octane in an engine designed for low octane fuel, doing so does allow you to crank the ignition timing up a wee bit, which can make the engine feel like it's running better overall..


|UPDATED|4/3/2012 9:59:58 AM (AZT)|/UPDATED|


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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

 WELL, I followed the rules, hooked the line to the "T" behind the carb on manifold. I have a consistant 18 lbs of vaccume. My problem is the WINDOW for adjustment is soooo wide. The carb screws move a considerable distance before anything happens. As for the timing, it also has a large travel with no movement on the scale of lbs. My timing light is broken, bulb is blown, so I guess I have to go back to a light.  Any other suggestions welcomed.  THANKS

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Mark, have a read thru Ben's "I HATE timing lights" thread. He also posted a different thread on setting the timing using the vacuum gauge method that it excellent, but I haven't found that one yet. I used to have them bookmarked on my OLD computer. Take a look at this one...it might help some, for now.
Lots of old members on this thread, too...ain't seen/heard from a lot of them in quite some time...

https://www.c3vr.com/vrforums/message193108.html#198002


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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

   O.K. I'm still in the dark. I have looked at the "Hate Timing lights" thread, still have a problem. Is it possible that I need to change the springs in the distributor? I have a consistant 17-18 lbs, with a very wide window on movement with timing.  What R.P.M. are you using? I am in the 800 range, and still have issues. THANKS

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https://www.c3vr.com/vrforums/message197065.html#197364

https://www.c3vr.com/vrforums/message244176.html#245113

Here's a couple more threads on the subject....see if any of it helps.


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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

  THANKS Joel.  A bottle of Pepto-Bismol and a good nites rest, maybe I can digest some of that info. 

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The basic gist of Ben's vacuum method is this: "

set INITIAL timing to the minimum required to get peak MANIFOLD vacuum.  you can turn your initial up further without vacuum increasing...  dont do this. turn it back down until it drops from peak..  then back up to barely reach peak.

this gives you the BEST off idle response."

If you have a worn distributor, or other things going on, you'll need  to tinker some more with it, but...this will get you in the right ball park.
Are you using a timing light? I have a really high dollar dial-back light that I hardly ever bring out anymore. I use Ben's method to set it. I use the light to tell me where it is that I set it, for future reference.
What issues are you having, anyway?


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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"