Bolw By ???

Perhaps we are just looking at it diffrerently. If there is no vaccum reading at WOT, there is no pressure differential? More importanly, in a vaccum secondary carb...how do the secondaries ever open? There is always a pressure differential. Zero inches of vaccum on a gage indicates 14.7psi (at sea level) pushing down on the carb. In the PCV, like the vaccum secondary port, it is the motion of the airflowing past the port in the base plate, rather than the sucking of the pistons, that creates the lower pressure.The valve is set up to provide more air flow as the vaccum drops. So in situations where blow by is the worst (low vaccum, climbing hills, towing...basically under load) the valve will move the highest amount of gasses It always flows some at WOT. It's just not pulled in by the same force.