Is it normal for a properly functioning PCV valve to cause a slightly rough idle? When I plug off the PCV the idle smoothes out and idle speed jumps up 100rpm. This is the second new PCV I have tried, both the same. Also the hose is new.

The motor is a stock 305, with a freshly rebuilt QJet, and headers. Both PCV have been the universal cheap Fram type. Should I try another brand?

Also the PCV is hooked up to the normal constant vacum port at bottom front of carb. I am thinking I should be able to hook it up to the ported vacum above the fuel inlet. Which I belive is normally the purge port for the charcol canister. Anybody see any problems with this? I'll try it and see what happens.

Thanks
Steve

ttt

a pcv valve is just a controlled vacuum leak. it causes the mixture to lean out a tad, which causes the lower rpm and slightly rougher running. it NEEDS the full vacuum to do anything, so don't hook it up to the big vent hookup on the front of the carb. if you can't get the thing to run right with it, then get rid of it and put a breather there and wipe oil off your engine from time to time.

wanarace,

My guess is that your idle mix is set a little too lean. That's why when you plug the valve the idle picks up. Try re-setting the idle mix with the valve installed.

If you can feel a vacuum at the breather location while the engine is running and PCV installed, then it is working.

The PCV is designed to use one of the big, full time ports on the throttle body (bottom of carb).

Last time I looked, Fram and Standard Motor Products get their valves from the same place. I've had good luck with both.

I think I am going to go with a breather for now. The idle mixture screws are sealed on this carb. However I might switch the baseplate with another one I have due to the fact my throttle shafts are sligthly worn and may be leaking a little.

I just wanted to make sure slightly rougher idle quality was the norm for the PCV.

Thanks for the help.
Steve