ORIGINAL: Artisan
When running crankcase pressure, a one way valve must be used, otherwise the end result is no pressure at all, since the piston goes up and down, causing the pressure to swing from positive to negative to positive over and over again.
Crankcase pressure should not be used unless a pressure regulator is employed at the carburetor.
Ed,
I am afraid you are not completely right.
What the tank 'feels' is not the pulsating pressures, but the average pressure.
This average has been found to be negative (sub-atmospheric) at low throttle openings, which may cause the engine to draw fuel through the 'pressure' line...
At high and at full throttle, the average pressure can be as high as 5 psi.
If you connect several inches of fuel line to that crankcase nipple, the volume of the fuel-line will be enough to completely dampen the pulses. This is why a pressure pulse operated pump needs a short line, with a relatively large diameter.