I bought a 400ex and replaced the main jet and pilot jet already. The quad came with a slip on exhaust and never ran right. When i push the throttle i can only push the throttle half way then it bogs down and shuts off. I had this issue with another quad and put bigger jets in. I already put a Keihin Hex Main Jet 160 and a 42 pilot jet do you guys think i need to go bigger? I have a K&n air filter on it and the top of the air box has three 3/4th inch holes in it from the previous owner.