I'm in process of cleaning up all of the electrical and vacuum lines in the engine bay. The car does have a check valve of sorts, maybe a PCV. I read differing accounts of whether or not a 74 should have one or should it just be plumbed without?
And I've gotta say, it sure looks nice in there without any vacuum lines!
Rob

You should run one IMHO. Otherwise stock up on valve cover gaskets.

The 74 was a passive vent system into the air cleaner. I prefer the positive flow on my motors (like the 73) but if passive was good enough for Porsche/VW...

You need it.
1) you don't want to vent that to atmosphere
2) gaskets
3) engines last longer if those gases are not in there too long.

PCV not PVC

One is a valve the other is plastic pipe.

Not sure exactly when the changeover was, but every 74 I have had has the PCV getting suction from the plenum. 75+ had the larger passive vent to the air cleaner.

To properly remove it though you will need to swap both your plenum and airbox to later parts.

I think there are pros and cons to both, the biggest con of keeping the PCV now is that new/good ones are near impossible to come by.

Post pics of your plenum and I can tell you what you have.

The last 74 I looked at was passive but perhaps it had been messed with.

Thanks guys. This isn't the best picture, looks like a valve but confirmation would be good.
Click to view attachment

That little circular thing next to the oil (or "oel") filler neck is indeed a PCV valve.

Clean it up and plug her in....

That is indeed an early crank case vent system/PCV valve.

It looks like your intake plenum is the later style though (based on the thicker throttle cable bracket) and that presents a bit of a problem as the later style does not have the port necessary to attach the CCV to it.

You can verify this by checking the two ports on the side of the plenum. The late style has a large and small port, the early style that is needed has two larger ports.

Not sure what airbox you have but you will need the matching early style as well.

Click to view attachment

Yes, but pvc could be pcv

Dislexia is not something to laugh at. Although feel free to laugh at me! Positive Crankcase Ventilation from the 70's,
Sheesh