Lean fuel mixture is the reason so many motorcycle engines seize when ice raced: they run too hot. When the temp gets colder and the air gets denser, richen the mixture accordingly. That was my reasoning anyway. The excess fuel absorbs heat. As for the timing a retarded ignition produces less power, hence less heat. If you can quote a text book to the contrary I'd be grateful.
Jetting as received (I bought it used and the bike was dealer prepped) was a 122 main (I think 118 is stock) and I went to a 126. The plug color with the 118 was brownish black so I figured it could go richer and might run cooler. Coolant level after the fire was up there; it didn't lose a drop. Pump impeller is OK and I checked the thermo-switch in hot water, it's OK too but I don't know at what temp it opened. Radiator was clean and unobstructed.
I've since installed a manual switch for the fan instead of the thermo-switch. After I start it and it warms up a little I'll turn it on. See if that helps the pipe run cooler.
Thanks for your interest.
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