Hi Guys! I see that this is an old post but i really need some help with my quad. I have a 1999 Honda 400ex that has been bored over to a 440 with stage 2 hotcams. I also have a pro circuit exhaust and a Uni air filter. I am having the same issue as many of you where it will start up and idle fine, but when I rev it up it spits and sputters. It also misses a little when its running. Right now i have a 190 main jet and a 55 slow jet, and the mixture screw is 2 1/2 turns out. It seems like it is running a little rich due to a brown/blackish plug, but it also seems like its not getting enough fuel. It does not smoke at all when it is running, just the little bit of white smoke when i start it up. My compression is at 120 psi. If you guys have suggestions PLEASE let me know because this quad is driving me crazy.