ORIGINAL: Pull Up Now!

That's 8mm venturi. Could be better but should work for a first project. Will lose 500 or 1000RPM. My 180 was a lot slower with a 22/64 venturi []


The lack of accelerator pump is a big deal. Agreed. 2 Strokes don't seem to need it at all for aircraft, but this four stroke is a lot better (and easier to tune) with it than without.

Does your carb look like the pictures I linked to? Yes, the standard 2 stroke one without spring.

I've never quite understood how that return tube running from your carb back to the intake doesn't just attenuate your diaphragm pulses, both positive and the negative one. The dry side of the pump diaphragm, seems to me, should be isolated (except, of course, for the pulse line) so all the pressure changes act on the surface area of the membrane. Right?

I don't think so. The isolation has been removed so that any oil tends to keep moving and no blockage will occur. It is effectively pumped because of the small line size compared to the amount of air going through there. If I could draw it as an electrical diagram, I would have two resistor/inductors, same frequency ac voltage at either end and out of phase, with the diaphragm as a voltmeter in the middle!