Thanks downunder,

You've given me the missing piece of the puzzle. I was amazed at how dramatic the needle settings changed as I changed fuels, but with the difference in stoichiometric ratio between Methanol and Nitro approaching a factor of 3, I understand where the difference comes from. I've been running the same plugs as I've changed fuels and it's clear to me that I've been having problems with higher nitro across all my engines because I've been consistently running plugs too hot for the fuel.

Thanks for the info,

Dwight