If it is a 2 cycle and you have to clutch start it ,you "need" the solid support on the lower part of the chain ,,,,a spring tentioner "only" will allow exsess play in the top chain possibly allowing it to bunch up and inter the small (10 tooth) area locking the engine or worse ,damage the drive wheel/shaft(thread on here about 10 tooth wheel woobles),,,,,the spring teneioner should only be taking up the extra 3/4 inch play (to quiet it down)that is needed in the chain drive set-up