Ezanen

Hello

I have a FT-160 with two silencers (.91 size). Now the problem is that engine doesn't rev up fast enough with these mufflers, it "hesitates". It sounds like a two-stroke when it's tuned too lean. The engine does eventually rev up, and hasn't yet quit by itself in air, the lag in power is just too long. Tuning the engine more rich doesn't help, it only causes one cylinder to quit. Leaning the mixture also has no positive effect. Without mufflers the engine revs up as it is supposed to.

So can these mufflers be too "tight" for this engine? Would it help if I drilled the exhaust holes in the mufflers a little bit wider?

2. question: Is it possible for this engine to run inverted without great mixture variations?

Thanks
Ezanen

Edit:

Sorry forgot the other info. Prop is wooden 18x6 (don't remember the brand), fuel Morgan Cool Power with 10% nitro and glow plugs are standard (OS F ??).