I am looking for help from anyone who has been in our same situation. I bought a 03' stock quad 400ex and put a three brothers head pipe and exhaust on it. In doing so Ialso had them put a K & N filter on too. The local shop jetted it and had some difficulty finding the right jetting size. In the end they removed the top of the filter box and jetted it (don't remember the size of the jets) I have had problems with quad ever since. whether it would be my wife or I riding it, it starts to cut out at the top of first gear and second and third. It does that either on flat land or climbing a small dune. It isn't like we have it completely opened up and want more speed. I think it is improper jetting starving for gas or too much air. HELP Thank you!

Richard