Pete,
Never had a problem with pipe pressure on BVM and OS91 engines. I bought a used jet last year that had fan pressure. What I didn't like about it is its limited range of authority. Each time I went out I would have to set the transmitter knob to full lean, peak out the engine by manually adjusting the needle, then once in the air I'd have to rotate the transmitter knob to full rich in order to get a decent contrail. Yes it had the extra large fuel tubing.

After 10 or so flights I felt I had enough and converted it to pipe pressure. I initially adjusted the needle after conversion and have never touched it since. Now with the extra pressure, the same knob on the transmitter can take it from too lean to too rich regardless of the weather conditions. Now I start it up, peak it out using the transmitter knob, and take off. Once in the air I can richen it up as much as I want.

Joe