I decided to clean up the piston/bore as well as I could and put the new rings on, since they only cost me $10 and if I have to bore it out they are of no use. The compression is holding steady at 90psi and even with a few squirts of oil only makes it up to 92psi. I am convinced this thing should run with that value.
I put a timing light on tonight, as well as a dial gauge to confirm TDC. The flywheel is keyed. The CDI has a curve as pictured below.
According to the manual the timing mark on the flywheel should line up with the cast mark on the case at 4000r/min. The line on the left on the flywheel (marked TDC) is where the flywheel lands when the piston is at TDC. Ignore the blue mark on the case.
When rotating the crank with a drill (obviously not 4k rpm), the plug is firing at the blue mark on the case, which is about 90 degrees from the cast timing mark.
So at idle the plug should fire at 12-13 degrees bTDC, and at full advance 25 +/-2 degrees.
I need to confirm the ignition system is working as intended, Is there a "base timing" like there would be on a points ignition, or is is not possible with the curve of the CDI?
Does degrees bTDC refer to degrees on the flywheel/crank, if 1 revolution = 360 degrees?
It just seems as though the plug fire is just happening WAY too late after TDC to ignite the mixture. I should mention that I tested the CDI unit on a running moped and it is working.
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