Guys,
I flew the K&B 40 with the OS FP25 muffler today. Worked great. The motor was set up with a 0.275" venturi and K&B NVA (I found a few a years back, seem fine I use a piece of fuel tubing to seal the body to the spraybar), all else is stock 4011. Used 7% nitro, 26% oil 40/60 (C/S) fuel with an Enya #3 plug. Prop was a narrow blade 11x5, launched at around 9700 rpm. It was very strong, easy to start (pulled it through twice, 3 flips forward, 3 flips backward, attach battery spinner flip and go). The ship is a 42 1/2oz biplane about 600 sq in. Flew strong solid right on the 4-2 point and it stayed. Eric Rule is sending a tongue muffler that fits the OS FP25 with the 1 1/4" hole spacing, could save another 1 1/2oz. We'll see once it gets here.
Best, DennisT