I have a friend who owns a predator. he recently ordered a slip-on, drop in K&N, and jet kit from rath racing. We did the airbox mods and jetted according to the directions. But now it just dies down from half to full throttle. No back-fire just bogs. I have tried EVERY needle and main jet combination POSSIBLE with little to no change. It has to be something disconnected or faulty. I changed the plug - no change. What could it be? PLEASE HELP!