I've run into a rash of QJets lately with clogged up PCV systems. Not sure why, but that's what I've seen so I thought I'd pass this along. Everyone replaced the PCV valve but they still get oily goop up in the air cleaner. Why? Becuase the port on the front of the carb is clogged up with all sorts of oily schmutz from decades of neglect, forcing the oily vapors backwards through the breather pipe on the other side of the motor, into the air cleaner housing.

The PCV valve and the hose aren't the usual culprits- it seems the metal vacuum nipple on the front of the carb just LOVES to collect that stuff, eventually plugging it solid. But even a 50% restriction can cause problems- and I've run into a LOT of this lately.

It will usually be visibly choked off just pulling the hose off and looking inside, but not always.

How to fix- DON'T spray it out with carb cleaner and shove a screwdriver in there to force it through- that'll shove it all directly into the engine. Take the carb off and clean it out. You'll probably notice that there's even a bunch of goop built up on the gasket under the carb. It makes for a big 'ol mess, all around. Clean the carb, put on a fresh gasket and see if your oily aircleaner problems don't disappear.