The Stovebolt Site Forums The Shop Area Engine Shop 261 PCV valve

Now that my 261 has been in service a couple of weeks there are some quirks showing up. One is that the idle isn't stable. I wondered if the factory PCV valve (metal valve that screws into the vent tower and a copper line to the manifold) was at fault so I dismantled it and cleaned it and made sure that the parts were in the right order, spring, piston, body, etc. per the factory manual.There's even a spec for spring tension. No change. If coming down a hill into town with a stop at the bottom it tends to stall after the high vacuum descent. Other times rolling to a flat stop all is normal.

So I took my vented filler cap off and put my hand over the hole and felt a strong suction. Hmmm... like manifold vacuum suction. So after thinking about this for a few days I put the Uni-Syn is use for syncing carbs on the valve cover hole with the engine idling. The PCV system draws as much air as one of the carbs. Can this be right? I substituted a non-vented filler cap in the valve cover expecting the idle speed to drop. It did not. So I'll drive it around for a few days and see what changes, it anything.