Fascinating discussion. Thank you all. I do not get how the needle pressure is the same but the pick up pressure varies, should they not be equal at all times? Also the siphon effect in a tank high situation can be alleviated by routing the carburetor feed line with a loop from the tank down to the level of the spray bar and then back up to the level of the tank centerline, then to the carburetor. Unfortunately this would do nothing for inverted (tank low) flight and the "anti-siphon" effect would be the same.


What really confuses me is that regardless of whether the tank is set up 2 or 3 line, the engine continues to run both in vertical up and down orientation and the length of the fuel column, which is what determines the siphon or anti-siphon pressure differential, is determined by the distance between the tank and the carb. A 3 line system will smooth out the variations, but they will be present regardless. Since the distance between the tank and the carburetor probably exceeds the up or down distance of the "misplaced" tank described above shouldn't the system be able to tolerate the pressure differential induced by the tank position. Or is the point to also eliminate the leaning out effect of a vertical up position and the richer mixture resulting from a vertical down position? Seems the only answer in that case would be to use a regulator which as long as the required minimal pressure was provided to the regulator intake would provide consistent pressure to the carb regardless of flight orientation or tank position.

My last question refers back to the prior statement about a modified uniflow "can be made to work with a throttle with a bit of extra plumbing (you actually need two check valves)." See picture. Wouldn't this flood the muffler with fuel if the throttle is cut in a nose down orientation?