I had the same problem with my O.S. 91 FX Ringed last year. It sounds like you are slightly rich on the low end. To get a perfect low end/mid range, get your glow engine started and run it at full throttle ( Thats to clear the motor ) then go half throttle. VERY CAREFULLY, adjust the low end until you hear the engine smooth out. Keep turning it clockwize until you here it slightly decrease in power ( That means you are too lean ) so turn it back counter clockwize until you get that fast nice smooth RPM, then turn it 1/16 to 3/16 turn more, then leave it. Now throttle down for a bit and move the throttle at a good pace to full throttle.

Now it's time to adjust the top end. Once you have the top end set the way you want it.( Tilt the nose of the plane up, if you hear the engine rpm slightly increase, that's good.)

Now the real test after doing what I suggested.

Let the plane idle for about a 2 minutes, now slam the throttle forward. You should get a very slight hessitation, then your engine should go full power without coughing or quiting.

Ever since the President of my club showed me how to get the settings right on glow engines, I haven't had to re-adjust my engines either low end or high end. Matter in fact, that O.S. 91 I was writing about is in my Seagull Extra 260 and my high end needle is in my closed cowl, and I haven't taken the cowl off since the first and last initial needle adjustment.

Notice no hole or high end needle extention sticking out of the cowl in pic's below.





Now at times the barometric pressure effects the engine power slightly once and a great while, but not enough to effect the engine performance all that much. Ever since Tom taught me how to properly adjust my engines, I haven't had any embarrasing "Dead Sticks." Thank God for the "Old Timers" in this hobby.

Give it a shot, it really works.

Pete