I have a problem with my bike, bought it this summer and it rode fine until the temperature change this winter (Live at 5000 ft in colorado), After sitting for about two weeks it started backfiring, now it has sat for a while and wont start. Am I right inthinking the plugs are fowled up? Also, how the hell do I change the fuel mixture? Any help would be apprecieated. ALso what position would be the fuel shut off for storage ?