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Unread 01-05-2010, 08:52 PM   #1
Ken4444
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Great video on understanding & setting ignition timing

I ran across this video about setting ignition timing and thought I'd pass it along. The last couple of minutes of the video are tilted toward the MSD products, but the first 4 or 5 minutes are informative and well done:

YouTube - How to set your ignition timing

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Unread 01-05-2010, 09:26 PM   #2
desert_driller
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Ken4444. That is a great explanation of how to set timing. I respect and applaud this great video. I have done it the same way for twenty years. Of course, the goal should be to set timing to what the shop manual says. No more. Now I want to set my timing to what is my best performance. I use a vacuum gauge.

The vacuum gauge takes into account what gas you use in the Jeep. Is it 87 or 91 octane? Also, how are those cylinders? and what is your gas-air mixture? By the way, do you live at sea level, or at ten thousand feet? Do you use synthetic oil or 10w30? What is your spark plug gap? No other method can tune your engine to its best performance like a vacuum tune up.

First: Disconnect the vacuum advance from your distributor and plug it.
Second: Gently rotate distributor to find the highest constant idle vacuum.
Third: Again gently rotate the distributor to drop the vacuum 1".
Fourth: Tighten it and recheck your carburetor settings.

See you on the road!
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Unread 01-05-2010, 09:56 PM   #3
_Kyle_
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Great Video!
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Unread 10-09-2013, 10:40 AM   #4
JayCO
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Quote:
Originally Posted by Ken4444 View Post
I ran across this video about setting ignition timing and thought I'd pass it along. The last couple of minutes of the video are tilted toward the MSD products, but the first 4 or 5 minutes are informative and well done:

YouTube - How to set your ignition timing
Ken... I just read your entire build thread, and learned a ton! I'm about to do the Team Rush upgrade to my new to me '82 CJ7, and wanted to understand more about ignition timing. This link is fantastic.

Thanks!
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Unread 10-09-2013, 10:55 AM   #5
Matt1981CJ7
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Nice video.

Now they need to do another video explaining the vacuum advance, and the totally different function it serves on timing and engine performance.

Matt
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Unread 10-09-2013, 11:34 AM   #6
hp_lovecraft
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Quote:
Originally Posted by desert_driller View Post
First: Disconnect the vacuum advance from your distributor and plug it.
Second: Gently rotate distributor to find the highest constant idle vacuum.
Third: Again gently rotate the distributor to drop the vacuum 1".
Fourth: Tighten it and recheck your carburetor settings.
Would this work with an HEI on manifold vac?

I have my setup with ported-vac, and timed traditionally. (ie no vac advance at idle, etc). Everyone says that manifold-vac is better for the HEI, but I've never seen a good writeup on how to properly time it, apart from the "turn until it pings" method.

I already have a vac guage setup in the jeep. I installed it years ago when I thought I had a problem that it would diagnose for me.
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Unread 10-09-2013, 12:46 PM   #7
Matt1981CJ7
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I wish the "set timing with a vacuum gauge" myth would go away. Sorry, but it's a terrible way to do this simple task.

It's likely to lead to timing that is far too advanced, causing detonation. Get a timing light and do it right.

A vacuum gauge can be used to set air/fuel mixture with good success, but not timing.

Matt
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Unread 10-09-2013, 02:50 PM   #8
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Quote:
Originally Posted by Matt1981CJ7 View Post
I wish the "set timing with a vacuum gauge" myth would go away. Sorry, but it's a terrible way to do this simple task.

It's likely to lead to timing that is far too advanced, causing detonation. Get a timing light and do it right.

A vacuum gauge can be used to set air/fuel mixture with good success, but not timing.

Matt
Matt, you may be totally correct, but what are you basing your opinion on?

Will the correct timing not always create the highest vacuum readings?

Is the old adage use as much total advance as you can without causing detonation still correct? Or is there another way to create power?

I do not pretend to know the answer, I'm just trying to learn.
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Unread 10-09-2013, 03:22 PM   #9
Matt1981CJ7
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Scrapman,

I base my opinion on having tried the vacuum timing method on my ol' 258, and I know the results.

As you advance the initial timing at idle, the RPMs and vacuum will continue to rise well past 20* BTDC. "Backing it off 1" Hg", as the myth suggests, is still likely to result in an initial that's north of 20*. Nobody in their right mind would run a 258 with that much initial. It's likely to rattle like a can of marbles under load with that much. But don't take my word for it, try it yourself.

If you don't have a dyno, the best way for the average shade-tree mechanic to set timing is exactly as the above video describes....set the maximum total timing to around 35* at 3000-3200 RPM, then play with spring weights to adjust how fast the centrifugal timing begins to kick in.

Matt
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