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Old 06-25-2004, 08:41 PM   #1 (permalink)
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I left my directions at the shop. When checking the timing with Pertronix installed how do I adjust for not having the vacuum advance hooked up?
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Ken
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Old 06-25-2004, 09:38 PM   #2 (permalink)
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Not real clear on your question.

When you set initial advance, it's always supposed to be done with the VA disconnected. So, if the manual says 6 degrees BTDC, that's where you set it with the VA disconnected.

Did that answer your question?
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Old 06-25-2004, 09:45 PM   #3 (permalink)
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No
Normally the vacuum advance is hooked up and when you set timing you disconnect it. Now that I'm using the Pertronix the vacuum advance is disconnected all the time. Do I just check and adjust my timing as though I'd disconnected the advance? I think the answer is yes but wanted to make sure. BTW I won't be doing much until I get my dizzy freed up. I'm working on that now. Thanks for the input.
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Old 06-25-2004, 09:52 PM   #4 (permalink)
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The vacuum advance is never brought into play when setting initial, and full timing. It is only adjusted by road testing it. If you will not be using vacuum advance, then just set timing like normal.
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Old 06-25-2004, 10:00 PM   #5 (permalink)
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Quote:
Now that I'm using the Pertronix the vacuum advance is disconnected all the time.
This I don't understand. Why is the VA now disconnected Are you talking about a Pertronix distributor that doesn't have a VA cannister? Or, are you talking about having just installed a Pertronix ignitor in your old distributor?

Just to review where the spark advance comes from:

Initial advance + vacuum advance + centrifugal advance = total advance

So, if you aren't running any kind of vacuum advance, you will need some additional initial advance to compensate. Your total advance will end up in the 34-36 degree range. The amount of initial necessary to achieve that depends on the amount of VA (or not) and centrifugal advance. All advance should be in before 3000 RPM.

There, does that help a little more?
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Old 06-26-2004, 01:01 AM   #6 (permalink)
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Quote:
Initial advance + vacuum advance + centrifugal advance = total advance
Actually total advance = centrifugal + initial, with or without vacuum.

The stop in the base of the distributor determines how far the breaker plate can move. The distance the breaker plate can move is the total centrifical. Neither the vacuum advance nor the centrifical advance can advance the timing past the stop. It doesn't much matter, though, as there will be very little vacuum advance left by the time the centrifical is all in.

And I don't mean to be correcting you, but we should clarify that that IDEALLY the timing should all be in by ~3k RPMs, but that's not the case in any stock distributor that hasn't been recurved. Most stock FOMOCO distributors will never see the total advance because the springs are too damn stiff.
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Old 06-26-2004, 01:07 AM   #7 (permalink)
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If you're talking about a Pertronix Ignitor, it does NOTHING that stock points don't do, except they don't wear out like points. The Ignitor will have no effect on your timing nor on wether you run a vacuum advance.
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Old 06-26-2004, 02:00 AM   #8 (permalink)
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John, don't be apologetic for correcting me. That's what this forum is all about, and I don't operate on ego. The main thing is to get a question answered correctly!

With initial timing set per specs, and no VA, most engines will run pretty doggy at lower RPM. That's the reason I was throwing VA into the formula. Sorry, that was for simplification, and not mathematically correct. So, if the VA is eliminated (still not sure why that's the case here), more initial advance would be beneficial.

Of course, you're right about a positive stop which limits total advance. You're also right that some distributors may not have all the advance in by about 3000 RPM, but they will be pretty close. Thanks for your constructive corrections!

FWIW, when I installed my Pertronix, it spark-knocked bad upon initial start-up, before I even tried to move the car. I had to reset the timing immediately. I hadn't moved the distributor, just a simple install.
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