An old 1995 Yamaha 1100 Waverunner we just bought was running badly. Would not get up to full power. Felt like a cylinder was not firing but they all were. We checked everything we could but it would not run any better. Finally my son tried turning the fuel select lever from full on to part off while running WOT and it started to run great. 62 mph by the spedo anyway. Why did this help???