just get a full kit from the parts store. the $35 one comes w/ like 5 adapters.
also another reason could be the idle screw being set way too fast. when at idle, your bike should sit just fast enough to not cut off. if your bike revs real high at idle, try turning the idle screw counterclockwise.
have you adjusted your throttle cable recently? you might have adjusted it too tight.
also, if you rebuild the top end, i highly recommend boring over to the next step up. if you just replace the rings and hone, you'll have too much piston play and you WILL eventually have a chewed up skirt. which will lead to a bottom end rebuild. just drop the extra dough on a bore/hone and a new wiseco piston. you should only need to go 0.010" over.
might as well replace all the gaskets while you're at it. INCLUDING the exhaust gasket which everyone always forgets.