Ok guys, here's the deal. I have a Hangar 9 Showtime 90. For power, I used an O.S. .91 Surpass II (fuel pumped) with a 14x8 prop. The engine is new with very little run time on it. First off, I do know that the .91 is on the low end of the scale for power for this airplane but it IS within the range.

I took the airplane out to the field on Sunday for the first flight of both the engine and the airplane. After starting the engine and tuning the needle valve, the first thing I noticed was that the peak RPM I could get seemed to be lower than the RPM I achieved in my drive way. Unfortunately, I did not have a tach handy to test this thought.

But I did tune the engine up to peak RPM (by sound) and then gave it a few clicks to richen it up a bit. Then I lined the airplane up and headed down the runway. The airplane did fly but it took forever to get off the ground and once it was in the air it really had no authority. Like I said, it flew but it just didn't feel very powerful at all.

My questions are these. (1) is a 14x8 prop too much for that engine? (2) is that engine going to significantly increase in power once it breaks in a bit more? (3) what RPM should I be turning on that engine when it's tuned/propped correctly?

I am beginning to think that I'm going to have to pull that engine off of there and get something WAY more powerful to do the job. I don't necessarily need to hover at 30% throttle but I would like the airplane to at least have enough power to be sporty.

in the 14" range i ran 14 x 6 on my os-91
in the 15" i ran 4 pitch

never tried a 13" on the 91 but from looking at my above numbers hum, i would think the 13 x 8 would be the ticket especially since the motor is not broken in yet the 8 may be asking to much on that 14" deal.

I've got a Hangar 9 spitfire w/a Saito .91 on it and 13x8 was the way to go for it. I've got a Showtime 90 too with an Evolution 1.00 in it and it is awesome, it does that 30% hover thing easily and flies like its on rails. Reinforce the landing gear!!!!!! It isn't held in the fuselage by much at all and any little bump could take it out. I lost mine on my fourth flight after a 8" bounce on landing.

I love mine but i have a 125 sato 4 stroke on mine using 15%helio fuel {coolpower} and it does a fine job the plane loves power and does enven beter on 30% fuel

Your 14x8 prop should be fine, it's within the recommend range and no specific break-in prop is listed in the manual.

4-strokes are very difficult to tune by ear, trying to tune your engine without a tach is merely a guessing game. A good tach is about $25 and well worth the investment.

Your FS-91 II Surpass w/Pump is a ringed piston engine. It will require a bit of time to break in, and it will grow stronger as it does so.

It sounds like you just need to fine tune the engine with a tach and take the time to get some break-in flying under your belt so that things will settle in for you.

16 x 6 on a YS-120 love it