Low pressure sucks..........

[Terry Caron]

Or does it?
In a venturi, does low pressure suck out fuel, does the higher pressure in the tank push it out or a combination of both?

[Dan McEntee]

   Hey Terry;
      The crankcase vacuum pulls it out through the venturi, and if you use pressure, it pushes from within the tank also. Most don't have a problem with muffler pressure but you can over pressurize a tank, and restricting the muffler pressure to a desired level is an engine tuning tool. On each airplane, I try both pressure and plain suction and use what the engine likes best.
     Type at you later,
     Dan McEntee

[Dane Martin]

+1 on what Dan said.
My nobler has an OS 40 la and it actually runs better (my preference in run style) on suction than it did on muffler pressure.
My banshee with the same engine and same muffler is more enjoyable to fly on muffler pressure.

Kinda strange, but it's really about everything together as a combo.

[Terry Caron]

So (to use my simple terms) low pressure does not suck - high(er) pressure is just pushy.