first cold weather ride.

[Coolector]

I was out the other day, East coast Canada, -6 degrees c. The bike worked pretty good except when I let off it would sometimes "fast idle" then come down, didnt think it was too serious but the first time it happened I was suprised, "big spurt, holy @#$^&*(" Should I up my main jet a couple of sizes to compensate for more dense air. As well could the pilot have anything to do with the jump in rpm when I let off, since its operation is from 0-1/4 throttle?? Perhaps it is dirty.
Thanks

 

[fuzzy]

Yes, both will need richened....

 

[70 marlin]

Watch you jetting very closely, on the very cold days. I had my jetting set up for 0 deg. then went racing and had the temp drop to -10 out on the lake and cold seized my motor! You have to keep heat in your motor. I wished I had blocked off my radiator with some cardboard or something.