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Old 07-21-2022, 02:54 PM
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Cliff Cliff is offline
350 Buick
 
Join Date: Mar 30, 2002
Location: Upper East Tennessee
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Could my Dizzy be off a Tooth?

1977 Cherokee, 401 and QT. Prestolite ignition unmodified.

Pretty good running Cherokee but I have always thought my timing wasn't right. Doesn't run right when set to factory specs and always seems to be too far advanced. The motor "sounds" advanced but it accelerates okay (very slight stumbles sometimes) but it doesn't run hot which I would expect if it was off a tooth. A hot start is difficult sometimes, another sign of too much advance.

I have always blamed it on the Prestolite system but now it's time to really figure this out.

My Chiltons manual has the following diagram:

https://i.postimg.cc/fTCCzbdq/image000000.jpg

The squares on the dizzy cap indicate the position of the Prestolite cap tabs. This shows them between cylinders 1-2 and 3-6. Mine are not in this position but before I adjust I am curious if Chiltons is accurate.

My #1 plug wire also does not match the Chilton's diagram. Mine is sitting where #8 sits on the diagram.

The vacuum advance is pointing toward the radiator - if Chiltons is accurate the vacuum advance should be pointing toward the PS pump.

I would like to hear from anyone with a Prestolite system, if they could eyeball their cap and confirm the Chiltons diagram.
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Old 07-21-2022, 03:37 PM
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devildog80 devildog80 is offline
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Chiltons is what I want to do with mine, so the advance is not sticking through the PS belt.

That would move my firing order around the cap by one position, but still synched with timing.

Mine currently sits like yours from PO, as I am still working to get it running, then will make adjustments as needed.

I think you are ok, and little stumble might be your carb adjustment or jets?

Found that on my '81 CJ5 when I changed out the carb.
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'84 Grand Wagoneer, 401 V8 (.030 over), MC2150 HA Comp, 727 auto, Selec-trac NP229, AMC 20 REAR - D44 FRONT - WT 3.31, 4" high arc spring lift

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Old 07-21-2022, 06:15 PM
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Cliff Cliff is offline
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The carb is an Edelbrock that I have rebuilt. And I have good vacuum and eliminated a few small leaks. But I have considered that as a possibility.
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Old 07-22-2022, 09:51 AM
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Cliff Cliff is offline
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Devildog got me thinking, and I had to read a little on ignition timing.

IF - TDC and #1 on the distributor are aligned, my timing should be correct.

AND - if I can align the timing marks with the balancer notch, my timing should be correct.

Both of these conditions are present on my motor, so even if my distributor doesn't match the manual, my timing could still be correct.

Is this a reasonable conclusion? Am I missing something?
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Old 07-22-2022, 10:32 AM
wiley-moeracing wiley-moeracing is offline
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You should line up the notch on the dampener with the tdc on the timing cover, then align the distributor rotor to the #1 terminal on the cap by rotating the distributor after loosening the hold down bolt enough just to turn the distributor. This will get you in the ballpark for timing. You will then need a timing light to adjust final timing, after you disconnect the vacuum line to the distributor and plug it. Just make sure that #1 cylinder is at tdc and that you are not out 180.
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Old 07-23-2022, 10:55 AM
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babywag babywag is offline
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Quote:
Originally Posted by Cliff
Devildog got me thinking, and I had to read a little on ignition timing.

IF - TDC and #1 on the distributor are aligned, my timing should be correct.

AND - if I can align the timing marks with the balancer notch, my timing should be correct.

Both of these conditions are present on my motor, so even if my distributor doesn't match the manual, my timing could still be correct.

Is this a reasonable conclusion? Am I missing something?

Correct.
#1 can literally be anywhere you desire on cap.
lift distributor when TDC rotate rotor to desired terminal on cap drop distributor back in.
Just need to ensure plug wires match firing order for "your" cap #1
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