For break-in you want a big flat prop...large diameter, low pitch. I like an OS 'F' plug in it. The instructions say to not rev over 5K for the first few minutes. You want this guy to be slobbery rich through the first 2-3 eight ounce tankfuls. Very gradually lean it out over the next 6-8 eight ounce tankfuls. Yea...all on the bench. After the last tank you should be close to full lean. Go in and check/set the valves for proper clearance. Put it on a plane and fly it kinda rich for another gallon or so. I liked the APC 15x6 on mine. It turned 9200-9400 on the ground and made a massive amount of thrust. IMO, running ANY 4 stroke over 10K on the ground is not a good idea as it will unload in the air...then it will be going WAY too fast for all those moving parts. The only downside to this engine IMO is its weight...it's a real pig at over 26 ounces!