It all depends on the miles and type of use the sled has been through. In the secondary (the bigger one) there are two bushings that wear out and three little plastic buttons. I need to change my buttons every year. The larger bushing also usually gets changed yearly. The smaller one not so often. The primary clutch also has two bushings that can wear out. It also has pins, rollers, weights and shoulder bolts that wear out. The secondary is easy to do yourself if you are mechanically inclined. The primary requires special tools. and is best left up to a professional.If you have over 2500 miles on your sled. then the secondary is over due and the primary is due to be freshened up. this is just a basic guide line everyones riding style can change the intervals for service.
i don't know if i'd jump right to clutching here. 550 rmk's haven't been around that long, although its possible it has a ton of miles on it anyway. it could be the carbs thats making it bog down at 75% throttle. i'd say make sure they're clean and jetted right.
Celebrate Your Indepence With A Rocket...Ride Polaris
By 75% throttle you are running on the mains. So the only way a carb will bog you down when running on the mains is if they are the wrong ones or partially plugged(very unlikely)Did this problem just show up or was it always there. Maybe you have a fuel delivery problem.
Filter or pump.
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