I wouldn't bother with the pump if I were you, I haven't found that one is necessary. I have mounted my 91FX inverted in my U-can-do 60, it runs fine. When I was breaking in the engine I did find it was easier to start it with the plane inverted, but after the first dozen or so flights I haven't done this - the plane has over 40 hours on it now. I do lots of hovering, up to a minute or so at a time. I am using the stock muffler, if you used a Pitts muffler it might not give the same back pressure, and I believe the power is somewhat less. The big OS muffler sure is ugly, and it weighs alot, but I believe it works a bit like a small tuned pipe.

The only time I would use a pump was if I wanted to mount the fuel tank around the CG, which I haven't done. My approach is to try the engine without a pump first. Only if I am having problems that I can't solve any other way would I consider a pump.

I believe some people had problems with fuel dripping out of the carb. The worst I have had is a drop or two, no big deal.

Malcolm