The bushings in the primary wear out and cause it to stick which causes the higher engagement. The weight bushings are the main culprit but the main bushings should be replaced too. Your primary clutch should be rebuilt every 2000 miles.
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Mines around 4500 and its jerky i heard they come from factory jerky next year my uncles got a clutch package (goodwin clutch) thats suppose to be more torque more top end and smoother engagement. Suppose to be a lot easier on the sled so ill spend the 300-400 dollars for the parts. That jerkiness is hard on those drive parts[/b]
MOTOMAN, at 4500 RPM engagement should not be jerky. Don't take this the wrong way but I would guess any jerkiness is caused by you. After you get used to the sled you should be able to take off very smoothly. BTW the 600 non-APV twin doesn't make any HP at low RPM's that's why you need the high engagement and with all of the 600 clutch setups on here for around $100 I would never buy anyone's $300 kit.