Hi Is a 4 stroke the one you are talking about?, I have a 71 inch egde 540,it was fitted with a 120 TT pro RP, it was climbing vertical like rocket,I had the TT second hand and it was ratteling a bit so I thought the bushes were worn out, so I got miself a brand new 2 stroke SC 120, I tried it and I am very desappointed with the , power I ran 4 tanks allready trough, and still wanting to overheat a full power (revs drops) with a 16X6 apc (the same I used on the TT pro)so I still running it rich, flying does the same, flyes ok for the first 3 minutes, then the power drops, I dont know if is because still stiff, or because the engine is not good, in the ground gives around 8500 revs with the 16X6 which are ok, I dont know!!, andddd the rattle still there (is not the exhasut or the frame), I guess bigger engines do have more play on the bushing thant smaller ones!!!??. any sugesstions??