jzinckgra

My Feedback: (11)

I have an older os 25sf engine that has been giving me trouble lately. It doesn't seem to be attaining peak rpm. With a 9x7 APC and WOT on the ground, I'm only getting about 12,000 rpm. Looking at the specs for the newer 25FX (~18000 rpm), it would seem mine is not running up to speed. Anyone know what the peak rpm should be? Also, as I mentioned I am having problems with the engine while in flight. For awhile I as running the engine too lean and it overheated, but finally I was able to richen it up, but again, only to 12000rpm. The weird thing is when I turned the needle valve from that position, I needed to turn it almost a full turn before there was any difference in rpm in attempt to run at peak. This doesn't seem right. It's like the needle just isn't sensitive to tuning until it becomes too lean then overheats. I think I might have a leak somewhere and might just replace all the gaskets, but finding replacement parts for a 13 yo motor might be hard.

flyn4Him

You might want to try a 9X5, 9X6 prop. I have a 25FSR that would spin a 9x6 at about 13,500 and 15,000 with a Mousse Can Pipe using 10% Riches Brew.

In Christ,

Joel Chavez

jaka

Hi!
Your OS .25 SF is perfectly normal.......12000rpm on a 9x7 is good ..the problem is you!
You are running a too large prop ...9x6 is better.
Just because a manufacturer say 18000rpm that doesn't mean the engine will rew that much with every prop you put on it.....most likely OS used a 7x5 or 7x6 prop when obtaining these rpm figures; Which on a normal airplane for this engine would be useless.

Regards!
Jan K
Sweden