One of our Chilean hobby stores is having a good deal on OS engines. I want to get a new 91 4-stroke for a 60" pattern plane.
I have had experience with a 26Surpass and a Saito.72, and this time I'll go with OS because it is on sale much cheaper than the Saito91. (I know the Saito is lighter!)

Questions:

I see the 91Surpass is offered in a pumped and non-pumped versions. Now, IS the pump really-really worth the BIG price difference? (almost 1.5 times!!!) Are there any other differences besides the pump&carb???

Anyone with experience on both engines?

Thanks a lot for your help!!!

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.

I have the unpumped OS 91 Surpass 2 engine with about 65 flights. Never had a deadstick! I use an APC 14x8 prop (turns approx. 8000 rpm). I also use a Graupner 3 blade 14x7 (turns 7600) this is actually too much prop, but the plane is very light (UltraStick 60). I use Byron 15% 4stroke fuel (16% oil). Idle with the 3 balde is an unbelievable 1400 rpm). I have 2 Enya 1.20 4 stroke engines with pump (geared pump). The only advantage is once you set the needle you harly ever have to adjust.