VPV valve testing

[Oddy]

Hi. Is there a way to test the impco VPV enrichment valve to verify its working properly? It is on an impco e converter and 425 mixer. Can you use a vaccum pump or something? I am asking because it came disconnected.(not sure why)

Thanks

[C3H8]

It is fairly easy to test. The VPV valve is normally open. Disconnect the vacuum hoses. Unscrew it from the regulator port. Either blow through it from threaded end or use low air pressure from an air hose. Air should pass through it. Next apply vacuum to the smaller hose fitting. Try to blow through it again. You should not be able to as soon as the vacuum exceeds 3" mercury. A VPV is in an open position anytime the vacuum being applied to it is under 3" mercury. Si it is open when cranking to enrichen starting mixtures and it is open at WOT when manifold vacuum drops below 3" to richen WOT mixtures.

[C3H8]

Should have added. This enrichment through the VPV allows you to close your power valve maintaining more controlled mixtures when applying part throttle to climb grades unless the grade is steep enough to demand full throttle.