Any ideas in this. Stock Polaris 700 I have lost some top speed used to be 60-63mph? Now tops out 50mph at around 6200rpm? I have changed the belt,fuel filter,and plugs. Completely stock except for K&N airfilter. 2004.5 model low miles and hours. I did put the stock air filter on same top speed loss! Been thinking clutch prob,one person told me to take a marker and mark the clutch sheave from center to ouside of sheave,if mark was not gone, after running top speed he said not upshifting all the way? If so ,what do I need to look for?Thanks!