Sounds like your clutch spring is dead...stretched that is. The clutch stays engaged so it won't sit still and idle, but it runs under throttle just fine...

A buddy of mine has one and his clutch springs failed much earlier than they seemed to have should. Use this spring, it'll last longer and you don't have to buy new shoes like if you go the duratrax route...plus it's under a buck and the duratrax piece is about 7 bucks ...

http://www2.towerhobbies.com/cgi-bin...?&I=LXWZ31&P=Z