Originally Posted by Golden69
Let me see if I understand.. Say if I set my initial timing to 10. Then I rev the RPM to 3500 or so and I check the Mechanical timinig at that point. I assume that I will use my timinig light and adjust the dial until the timing mark hits zero. If the timing gun is set to 20 and the timing mark is at zero, then the mechanical advance is 20. This is added to my initial of 10 to give me 30.
To determine the vacuum advance, I plug in the vacuum advance hose while the RPM is at 3500 and note the change. If the change is +5, then this number is added to my initial(10) and mechanical(20) to give me 35. Is this correct?
What is the optimum number for each value: Initial, Mechanical and Vacuum? Does it matter if initial=15, Mech=15 and Vac=5?
How is Mechanical Advance adjusted? In your statement you mentioned springs. Assuming that you are checking the timing at the same RPM, will softer springs increase the value and firmer springs decrease the value? Also, will different springs affect initial timing?
Back to the Pertronix question... Will differences in the gap between the magnetic ring and electronic module affect any aspect of timing?
Hold it - let's start over. When you set the dial at 20* and the timing index on the balancer is aligned with "0" on the tab, that's 20* advance, which INCLUDES the initial timing you set at idle; whatever you see on the dial with the marks aligned is TOTAL TIMING - the sum of initial plus the centrifugal the distributor mechanical advance system adds. That's the 34*-36* figure you're looking for with the centrifugal advance "all in". Vacuum advance has nothing to do with TOTAL TIMING, as it drops out when you put your foot down.
You check the vacuum advance operation at idle. If you have your initial timing set, say, at 10* (vacuum advance disconnected and plugged) and then connect the vacuum advance, the timing should jump to 25*, as the vacuum advance will add about 15* at idle vacuum (if you have it connected to manifold vacuum and it's the correct vacuum can for your application). That increase in timing will also increase the idle speed, so you'll have to set it back down with the idle speed screw on the carb throttle lever.
A good baseline to start from is 10*-12* initial, 24* in the centrifugal in the distributor, "all in" by 2800 or so, and a vacuum advance can that adds 15* and is fully deployed against its stop at 2" Hg. less than your idle manifold vacuum reading.
The Pertronix unit has no effect on your advance curve, and the gap between the ring and the module has no effect on your timing, assuming it's within Pertronix gap specs.
Weaker springs will bring the centrifugal curve in earlier (lower rpm), stronger springs will bring it in later (higher rpm). Properly-calibrated springs will not permit any centrifugal advance at idle rpm; you can check this by putting a rubber band around them and checking timing with and without the rubber band in place - it should be the same.
E-mail me ([email protected]
) and I'll send you my "Timing 101" paper - it'll take the mystery out of this stuff and explain it in layman's terms. It's here on the site somewhere, but I don't recall where.