From what i've heard and read this is a common problem with the 1500's. i've also heard the thunder clutch fixes the problem, i've ordered one. you need to buy an aditional clutch spring and use your old one, i just purchased two new ones. my clutch has been on order for a few months now, i talked to a guy and thunder and he said hes still waiting on cores to come in, and i could send mine in and he could have it machined in about a day, but weather like this in wisconsin doesnt stick around for long, so i'm just going to wait, mine isnt that bad yet.
hope it helps.