Regulators...
I have 2 of the Cline's and one is on a 2 stroke and the other is on a 4 stroke. Muffler pressure on 4 strokes works fine, remember the pressure is checked and retained in the tank.
From what I know of 4 strokes the crankcase vent is just that, a vent, it sucks air in as the piston rises and blows it out as the piston falls. Blow by from the piston ring does enter the crankcase and the oil that is in it exits theengine through the port. With all that being the case the crankcase on a four stroke isn't exactly a great source for pressurizing the fuel system.