Flypast111

Non-exhaust pressure fuel delivery to a CL venturi requires that the engine generate sufficient vacuum at the venturi spraybar to "suck, or draw," the fuel into the engine. When a properly placed fuel tank (i.e. half of fuel level above the NVA and half below the NVA) is filled with fuel, gravity assists the first half fuel delivery and works against the second half remaining fuel delivery.

For a CL engine with sufficient fuel draw or suction (i.e. vacuum), the engine will generate adequate vacuum at the venturi spraybar to draw fuel into the engine without additional needle valve adjustment to sustain HI rpm operation. In this case, the 6x3 wood prop application did not achieve such a result. Additional needle valve adjustment was required to sustain HI rpm operation for the lower half remaining fuel to be consumed ... else, the engine would likely stall (or at best run slowly for the duration). On the other hand, the 5x3 nylon prop consumed the entire 2oz tank without further needle adjustment.

Further, I agree that the "fuel delivery apparatus" is also key to achieving adequate fuel delivery. So, close attention to the entire fuel delivery system is required. In other words, an improperly placed fuel tank or a long fuel line will also impede fuel delivery.

Cheers, Flypast111