I have not run across one that had a clutch. My own and the several I have been around were all direct drive. If the unit is brand new as long as the head is free my guess is the low speed screw needs adjusted or maybe both the low and high. If it is used I would make sure the air and exhaust is open and the fuel system is good from the filter to the carb and there is no bindup on the head or drive shaft and if all thats good I would look into getting the carb adjusted.