I am posting for my neighbor. We went to Hatfield McCoy this weekend and his 02 Sportsman 500 started great, ran great at low throttle, ran great at WOT, but at mid throttle it ran smooth but was acting like it was hitting the rev limiter when riding in high gear. The quad behaved this way riding on flat trails, hills, and even if he got hung up in mud or against a rock. If he left off and then punched the throttle it ran fine. Again the quad was not running rough or cutting out, just acting like it was hitting the rev limiter. Is this related to the clutching or any other ideas where to start?
Thanks!

 

Could be as simple as a little water or trash in the carb that collects at the bottom of the bowl.I've seen them idle good,stumble mid range when it gets a dose of water,but runs good on top end when it allows more clear fuel.May or may not be the problem,but open the drain screw at the bottom of the bowl,drain fuel into a clear container and see if water is present. It will accumulate at the bottom if there's any. With the fuel we get today,not a bad idea to run an ethanol treatment,only takes about 1 ounce per 5 gallons of fuel for maintenance measures. If it still stumbles,then I'd check the belt for any worn,glazed spots and blow out accumulated belt dust in an open area. Make sure the plastic jam nut isn't loose on the front clutch. If it backs off too far it can limit,but usually limits on the top end. The rpm limiter itself on this model is built into the speedometer.Item#8 is the jam nut. Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse