bdmartin

The backfires are probably from too much fresh oxygen in the exhaust. Check the air injection system that I mentioned before and check for exhaust leaks.

Leaning out the mixture is only possible for the idle circuit - screwing it in (clockwise) will lean out the mixture.

I would retard the timing to 2 degree's or even 0 for the test. Retarding the timing will drive up the cylinder temps to your benefit.

GD