i have been trying to figure out what going on with my sled. It seems it doesnt want to run over 4,000 rpm. the plugs are black like black black. i have gone through reeds, ves valves, sprayed fuel into the carbs, drain fuel, sparkplugs and so on, i have also replace the temp sensor which most people said should be wrong. any other ideas would be great. sled starts like a polaris, and idle's just fine. but once it hits around 4rpm it back fires and studders.