I have a new one (63FZ). Dave Shadel told me to prop it to turn between ten and eleven grand on the ground (after an hour or so of running), then back off a click or two (rich) on the big needle.

According to him, the 63 likes to turn up faster than most other four strokes; including the other YS's.

My 91FZ with an APC 16x6 is turning 8700 on the ground, and seems to be very happy; likewise a buddy's 91FZ. The thing you don't want to do is load the engine down too much; that causes overheating.

I was concerned that the 16x6 might be too much prop, but I'm running rich (distinct, but not heavy, smoke trail in the air) and there are no signs of overheating.

He was specific about this on the 63; too low an rpm is not good.

Steve