Update...
I've done some testing in the actual circuit. It seems that Dwell_Time works 100% at a setting of 2 uS. At a setting of 1 it seems to work 0% to about 80% of the time.

This could be because I'm using some fairly long wires to connect the processor into the circuit. But I suggest that about 5-15 uS would be a good, safe value.

The reason to go larger would be to give the LED time to flash. If you're using the LED you'll probably want to use a much larger value forDwell_Time.
I don't have much use for the LED for timing, and I don't think it will give very accurate timing values since you'll get a smear from the time of the spark till the dwell time expires. I think that would lead to the mark showing up looking like the advance is less than it is.


-Jake<br type="_moz" />