My trusty OS.45 FSR is a little under the weather these days. She just wont hit peak rpms.[:@] I've checked fuel lines/tank and filter. All are ok, no air leaks or debris. It runs fine and transitions smoothly to about 2/3rd throttle (which is more than enough to fly my plane). I did notice that when I pinch the fuel line momentarily, the engine peaks right out to max rpm and then slows down again. Sometimes, if I keep the throttle wide open, it will reach peak rpm. The pressure tap on the muffler is also clear of obstructions.

The engine was stored for about 20 years NIB in my closet and only recently put into service early last spring. I'm running Omega 10% Nitro fuel. I'm kind of suspecting bad O-rings in the carb. which is a model 4B. The Needle valve O-ring seems ok, but when I added a small piece of silicon tubing to the end for a better seal, it runs slightly better. I have had the carb. off to check for debris and it's clean.

Any ideas?

Thanks,

Scott