Thanks to both of you!

Makes sense. Since you run leaner and hotter with more nitro you can/should run a cooler plug. It never occured to me before, but more nitro and /or a hotter plug should ignite the mix earlier in the stroke - advancing the timing! Too much advance and you get a backfire. So if I wanted to run higher nitro in my 4 strokes without the backfire problem, then I should go to a cooler plug - Is this correct? I wonder if a cooler plug would help the idle in my 2 strokes as well.

Dwight