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When setting the dwell, do you also disconnect the vacuum advance? I know I do this for timing, even have a machine bolt that I keep in my bureau for it (to make sure it doesn't get into the OTHER mix). But I'm not sure whether to do it for dwell. Also, the chilton's says 28-30 degrees, but a local been around the block since the 50s mechanic says he puts them at 32. I have a 70 Chevelle with a 307 and 4bbl setup, running between 12-14 timing and have rapidfire plugs.
Thanks in advance!
Fred
 

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The vacuum advance should have no effect on the dwell reading unless the distributor has some worn bushings, etc. If I remember right the higher will allow for some point wear. Your timing sounds a little too much advanced, but if it runs well, must be ok. tom
 

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Riffers70

Set the dwell at 28, as the points rubbing block breaks in and wears down the dwell will increase to 30, 32, 35, etc. When it gets up around 38-40, the car will start to run bad. When it gets over 40 the car will quit because of no point gap. Each degree of dwell gained is a degree of timing lost, by the time it's gone from 28 to 36, your timing will retarded 8 degrees from where it started. This is why mechanics set the dwell first and the timing second. I don't think your buddy understands what's going on here....

Tom
 

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Mike: Dwell is the angular measurement of the "time" that the points are closed. This describes how much time in degrees that the coil has to receive power from the +12 volt supply. The longer the dwell the better the coil is charged or saturated. This does not become important until you get to high speeds and there is not enough time to get the coil fully charged up for the next spark.
 

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Riffers,
I might just mention, there is an electronic conversion kit on the market which is made by PerTronix, called the Ignitor. It totally fits inside the distributor cap, has only 2 wires going to the coil and eliminates points and condensor forever WITHOUT modifying the distributor (if for some reason you ever wanted to change it back). I have them in all my engines and several of the people at this site have installed them on their cars. The best part is that you have an electronic ignition without altering the stock appearance.

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