The ball in the PCV valve is basically a one way check valve and it's purpose is to close off the valve from the crankcase side (or valve cover side) in the event of a carb backfire that could conceivably shoot a flame through the valve and into the crankcase (or valve cover wherever it is mounted) and ignite the gasses in the engine.
PCV's are rated differently with a primary concern to how much vacuum it takes to unseat the ball and allow gasses to flow to be reburnt in the engine. Most take very little vacuum.
They are also sized to allow control of the amount of suction they can pass.
In our stovebolts, too large of a PCV will allow too much vacuum flow which effects the vacuum wiper operation (if equipped).
I installed a PV1053 in my modified draft tube and it works great and doesn't effect the vacuum wipers.
I tried a larger PV233 and it effected the wipers to where they wouldn't work, it diverted too much vacuum flow away from the wiper motor.
I adjusted my carb via the vacuum gauge method and on my 216 I get a steady reading of 19 at 450 rpm. Same as before the PCV mod.
The PCV mod seems to work fine for my 49 216 at all speeds/rpm.
Dave
