ENGINE TEMPERATURE,,,, FUEL QUALITY (when I mean fuel quality, I am NOT refering to shell or BP or 87-93 octane), AMBIENT temperature, RIDING CONDITIONS, MODIFICATIONS,,, INHERENT EFFICIENCY PROBLEMS with YAMAHA"S engineering department,,,etc,,,etc,,,etc,,, HAS to do with "dirty powervalves".... I don't want to get into WHAT IS IN A GALLON of gasoline, because I would lose 98% of you guys!!!! Theres additives that "resist vaporization" and also "promote vaporization" depending on the time of year and the AMBIENT conditions of the AREA IN WHICH you purchase fuel... You could buy your fuel in the mountains of montana and idaho and bring it to WISCONSIN and run it in sled #1 (a 2002 viper) and run wisconsin fuel in test sled #2 (the EXACT SAME 2002 viper) and spend a day riding the test sled #1 and another day riding thet sled #2 and come up with a BUNCH OF DIFFERENT findings BETWEEN THE SLEDS!!! MOBIL oil cmpany is NOT going to tell you exactly WHATS in their additive package!!!! neither is BP or anyone else... !!! I am not going to get into it either for the sake of some of you trying to purchase some of the additives (they're out there,, you just need to know where to look to find them)... Theres idiots out there than go to the local MENARDS or HOME DEPOT and buy a gallon of MEK (methyl ethyl ketones) and try and make themselves a racing concoction and get injured or even killed because they don't know what their doing.. I don't need the lawsuits!!!! Yeah,, NOSBOY told me to burn MEK in my sled,,, I left it in my fueltank and when i came back in SEPTEMBER,, my sled was destroyed!!! NOT A CHANCE!!!!