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Old 11-13-2010, 09:19 PM   #1
bweaver999
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Default Too much timing symptoms?

Other than pinging what does too much timing do? Just put in a new Mallory distributor with vacuum advance. Replaced the mechanical only. Took it for a run before connecting the vacuum and it ran the same. With vacuum connected, at steady throttle (most RPMs) it seems to miss or breakup just a bit. Stand on it, she fly's and seems to run fine.

With out vacuum, 18 degrees at idle (850 RPM), 36 at 2800 RPM.

With vacuum, 36 at idle, 52 at 2800.

I don't hear any pinging, course the side pipes may cover any of that up.

I think it's all adjustable, will play with it some tomorrow. Plan to drop it down a few degrees for start although I think 36 mechanical is where I want that.
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Old 11-14-2010, 01:29 AM   #2
MikeM
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Quote:
Originally Posted by bweaver999 View Post
Other than pinging what does too much timing do? Just put in a new Mallory distributor with vacuum advance. Replaced the mechanical only. Took it for a run before connecting the vacuum and it ran the same. With vacuum connected, at steady throttle (most RPMs) it seems to miss or breakup just a bit. Stand on it, she fly's and seems to run fine.

With out vacuum, 18 degrees at idle (850 RPM), 36 at 2800 RPM.

With vacuum, 36 at idle, 52 at 2800.

I don't hear any pinging, course the side pipes may cover any of that up.

I think it's all adjustable, will play with it some tomorrow. Plan to drop it down a few degrees for start although I think 36 mechanical is where I want that.

Sounds like you need to lose some low speed advance. Cut the initial back to about 12* or take 5-6 degrees out of the vacuum advance.
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Old 11-14-2010, 08:56 AM   #3
Vet65te
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BWeaver999 - Does you distributor have an adjustable vacuum advance pod? The adjustable types, some came stock with MSD and Mallory distributors and no doubt others, are usually 'hex-shaped'. Using a small hex wrench inserted into the nipple you can adjust the amount of vacuum advance by turning the interior screw one full turn which typically increases or decreases the total by about 3 degrees.
Mike T.
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Old 11-14-2010, 09:12 AM   #4
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My experience with too much timing is that on hot start you will get resistance in attempting to turn the motor over and you will also get surge at lower rpm.

Rich
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Old 11-14-2010, 02:39 PM   #5
bweaver999
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My experience with too much timing is that on hot start you will get resistance in attempting to turn the motor over and you will also get surge at lower rpm.

Rich
Surge is the description I was looking for.

Found that the vacuum advance does have adjustment. It is an allen set screw buried inside the the hose nipple. Took about 6 degrees off the idle (now at 30 and it's down some across the RPM range). Now she is running fine. Just waiting for summer to get here and see if it helps keep her a bit cooler when idling on a hot day.
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Old 11-14-2010, 03:09 PM   #6
lars
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Your mechanical curve (18 initial, 36 total, all in by 2800) is perfect - it should give you an excellent level of performance.

As stated in my previous posts, modern pump gas will not support an 18-degree vacuum advance curve on top of an aggressive 36-degree total mechanical curve. Burn rates of modern fuels are quicker than that of the old fuels that these engines were designed for. Running 52-54 degrees of total combined timing at cruise will result in what I call "trailer hitching," with a slight "chugging" or "jerking" sensation. To solve this, don't touch the mechanical curve - your numbers are good. Just limit your vacuum advance to about 10-12 degrees rather than the 16-18 that is common on the vacuum advance control units out of the box. My paper on vacuum advance describes in detail how to do this with a fixed unit. If you have an adjustable unit, just adjust it to limit the advance to that number. You can e-mail me for a copy of the vacuum advance paper.

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Old 11-14-2010, 03:09 PM
 
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