OK, Lets review a few things,
Rich or lean refers to carb jetting not oil ratio.
50:1 oil mix will run richer than 32:1 and is not enough oil for your air cooled Blaster.
Your 32:1 oil mix is not causing your plug fouling. your jetting is.
Cold weather will lean you out. Cold air is denser.
The Yamaha manual says 90 octane or better.
Race fuel has more gravity and usually runs around 1 jet size leaner than good pump gas.
The stock or lightly modded Blaster does not need race fuel.
That said, I would do your top end, check your crank seals and for other air leaks, replace your reeds. Mix up your BellRay at 32:1 with some good 94 octane pump gas and JET for your mods and weather.
mix ratio therory does'nt really sound right at first, but Tim is dead nuts on the money, I've done alot of reading on these things, and suggest if you don't understand how Tim put it... do some reading yourselves
any book by Eric Gorr is good stuff and although old, Gram Bell's performance 2 stoke is good reading as well.
whoa I thought my compression was low at 120psi:-/