What's your experience with the OS .91fx? I seem to remember hearing that they're pretty unreliable. Any comments?

I got 2. I love them.

Been using one on my 4*60 now for 6 months and its been the one of the best motors I have owned.

Just my .02

I had one and it gave me nothing but trouble. Just couldn't get a consistent run out of it. I am by no means an expert, but have not had any real troubles with my engines before. Finally gave up on it. Do a search for 91 FX and you should pull up quite a few threads to read.

I have one on a 4*60 too and it's a great engine. Tons of power! About the only thing that's wrong with this engine is the rear needle valve (air leaks). That can be fixed real easy. Use a 160fx rear needle bracket and a needle valve ass'y from an old .40fp. About $15 bucks total. Makes it run like a top!
I e-mailed OS about it and that's what they told me to do, and I haven't had a problem since I made the repair. I know.... OS should have done this for us, but.... anything that's man made can have problems, and what's life without problems.... Death.... I'll take the problems anytime!!!
Suptter

I have had 3 .91 FX and everyone was a terrific performer. While Great Planes recommends either 13X8 or 13X9, this engine will pull a 15X6 with great authority.

If you take time to properly breakin the engine it will serve you well. It is an easy starter with great transition and pulling power.

My current one is in a U Can-Do 3D and it is well overpowered.

I owned two of them over a months time and turned them both back in. That is only my opinion of the 91 fx. However the rest of the OS line up is excellent.

Danny,
Do you remember what the part numbers were for the bracket and needle? I found the 1.60 FX bracket, but don't know for sure which needle to use. Thanks for any reply.

Thanks for the responses.

I seem to remember, from previous posts, that some people had issues with this engine. But I've also heard, from others, that this is a decent engine.

I'm still open to any responses or experiences that anyone's had.