OS 1.20 FS Poor Performance
 

I have a 1.20 FS that is only putting out 8200-8400 rpm on a MA 15x8 prop. I have replaced the bearings, piston ring, gaskets and set the valves to spec. Compression improved but maximum rpm still is below what I would expect. My understanding is I should be getting 9,000+ but not even close. The engine is 10 years old but with the rebuild last year, it should be as good as new.

Am I missing something or is that as good as I can expect?

Thanks.

RE: OS 1.20 FS Poor Performance
 

If your O.S. FS-120 is the old version with the two rocker covers, then the RPM level you're getting is about right. If you have an FS-120 Surpass, then it may be low on RPM. However, we've usually used a 15 x 8 APC propeller on our test stand, and see a little over 9,000 RPM. If the engine is really "right", and we have a good prop, we've seen the high 9,000's.

RE: OS 1.20 FS Poor Performance
 

Thanks Bill. It is a Surpass so I'll try an APC 15x8 and see if I pick up a few hundred rpm.