I am using a OS FS81 four stroke...It has ample power ..the thing that I like most about it is that it dosen't have a crank case vent like most of the four strokes do...It recycles its oil and lubricates itself somehow so it is very clean running and does not get near as much slime all over like all the rest do... It runs like a clock..It seems like it never needs tuning...You can usually start it by bumping it back against compression .