My 02 xc 800 is bogging down at 1/2 or 3/4 throttle around 5500 rpm, i went throught the carbs and rebuilt, changed all the jets etc keeping them the same as what was in them. raised the needle clip up one slot to the top but didnt seem to help at all. New plugs, pulled them and were wet. pulled the exhaust valves pretty oily, cleaned real well and re installed. None of this seemed to help. Checked the spark looked strong on both cylinders. Fuel is new. I haven't checked the belt deflection yet, could this be the issue? Looking for advice.