I guess the best advice is just what 98srx6 said!!!!! Yamaha jets their sleds REAL FAT to try to reduce warranty repairs... yes, you could rejet your sled and get a few more ponies out of her,,,,but,,,,,the nights when its 20 below and you've had a few pops in you, and you open her up on a frozen lake,,,you'd probably be pulling her home after she melts down!!!!!! in theory, your sled will run better in 20 below weather compared to 20 above weather!!!!! I fix a LOT of my friends 2 stroke saws and snowblowers... I tell them to ALWAYS mix 32 to 1 even if it tells them 50 to 1...because,,, IT'S CHEAPER TO REPLACE PLUGS THAN PISTONS!!!!! Gary Oles nosboy