I started my OS 91 Surpass wo/pump about 2 or 3 months ago. It is very reliable and turns a 13x9 APC prop with Tru-Turn spinner, 10% Cool Power, and the OS F-plug at 9200 to 9300 rpm. It has about 20 to 30 flights. I use a 13x9 prop because of ground clearance on a Ultra Sport 60. I have no on-board glow system. I have people come up to me quite often and ask why I didn't get a pump on the engine. This my 1st 4 stroke. I have flown many many planes with 4 strokes and have never regretted not owning one. I bought one and can't say I regret it but I wish I had a ST 75 or 90 2 cycle on my Ultra Sport 60.