The belt that comes on the sled is a 127 Skidoo belt and it is too soft and creates inconsistency in the engine rpm, the gold series belt is too hard of a compound. The best belt we have found and recommend for the sled is the Dayco Ultimax 2 belt and the correct belt is Part# 138-4332, not the belt that the Dayco book lists (144-4353). Also be sure that your clutches have correct center to center and offset. -- Bill