The Stovebolt Site Forums The Shop Area Engine Shop Carter YF 964S with a PCV system.

My GMC 228 came to me 11 years ago with a not-stock Carter YF 964S. It has a 0.099" jet and (I think) a 0.075" rod. Runs good as far as I can tell. Gets around 14 MPG doing mostly rural 40-60 MPH driving. AC R45 spark plugs are a light brown color.

I decided I wanted to install a PCV system.

I found a valve cover from a larger GMC truck that had a hole in the center for PCV. I installed a Standard Motor Products V237 PCV valve (recommended by a 'Bolter) in the hole and connected the other end of the valve to manifold vacuum. To provide an outside air source, I cut the draft tube off of the oil-fill tube and blocked off the hole where the draft tube had attached. Then I replaced the oil fill cap with a Mr. Gasket breather designed to plug into a V8 valve cover.

I started the engine, but it did not want to idle. Not surprising as I had just installed a vacuum leak. I backed the idle mixture screw out 1.5 turns and the idle got a lot better. I set the idle speed to 600 RPM (A/C season here, 90F today) and found I could move the idle mixture back in a half turn with no change in idle. I'll crank the idle back down to 500 RPM late next fall.

My question is "What do I do about mixture driving down the road with the PCV valve installed?"

About 5 years ago I did a temporary install of a digital Air/Fuel ratio (O2 sensor) in an attempt to tweak the carb for better performance. The darn thing bounced around a lot. I finally just went back to the original carb jet and removed the instrument. Should I re-install it?

Or maybe just keep an eye on the spark plugs? If so, should I start with a new set of plugs so the current light brown color doesn't influence my opinion?