Adam - with the valve in there, if it's restrictive enough [and it'll prolly be plugged if it's not changed regular], you might not notice any problems, tho the vacuum would likely be less than it should be - the main problem is a PCV valve should come off the crankcase, not the valve cover, especially with a vented oil fill cap as Mike's appears to have [can't tell if his has a valve] - mostly what's happening is it's drawing air thru the valve cover from that vented cap, instead of drawing fumes/oil mist out of the crankcase as a PCV is meant to do, and a PCV should go to a metered vacuum port at the base of the carb
Bill
