Bax, got another question for you...
We are putting a slimline pitts style muffler on an OS 160 FX. Tank is within an inch of the engine and centered on the thrust line. Now question. How much muffler back pressure is required to adequately to supply fuel? Can you give me a pressure figure in inches of "water column" at idle, mid throttle and full throttle. This would be easy to measure and give me an idea of how much to restrict the exhaust .
Hopefully some one has compiled this data and will save a lot of experimentation.

Thanks
Shepp

We're sorry, but we don't have a number for the pressure needed at the fuel tank to give good fuel flow. It's always been a bit of "try and see". Some people have used the muffler you suggest with no problems. Perhaps the fact that large-size plumbing was used throughout was what worked. Standard-size plumbing is one of the causes of low fuel pressure.