I'm a little confused about where to plumb the PCV valve. In the pic below, the newer hose comes from the valve. I suspected it went in the large vacuum port in the front of the carb, but the hose I'm holding went there before, and runs to the vacuum canister (in addition to the smaller line from the manifold). There is a tee in the line that had a small plastic fitting on it, which I've since removed and capped (seen in background). When I plug the old hose (to the vacuum can) into the carb, the wiper door and headlights work better and faster.

Can anyone make sense of all this for me?

Thanks!
-=Boston!=-

 

The PCV valve should be plumbed to the port on the front of the carb, at the bottom. There was a t-in that line with vacuum going somewhere else, but I forget where since I removed most of my stuff long ago.

The large line going to the canister should connect to the VENT line on the top / front of the carb. It is a non-vacuum line and is to vent the fumes to the canister.

hope this helps.

 

On a '72, the correct plumbing is for the main PCV line to connect to the port under the front of the carb. The hose then runs to a "T" fitting on the PCV valve on the valve cover. The other end of the T runs to the EVAP cannister. There is also a small vacuum line that runs from the EVAP to a manifold vacuum tap on the passenger side of the carb to the long vacuum tap that runs through the choke mechanism.

There is some creative room for the actual routing in this case since you could have a single line running to the PCV with a T anywhere in this line. The T doesn't have to be in the connection to the PCV, but that's how the factory did it.

Further, the distributor vacuum line runs to the timed vacuum port right under the throttle solenoid bracket. And the choke pull off runs to a vacuum tap on the front top passenger side of the carb.

 

Is the EVAP canister actually a vacuum canister? It's under the driver fender, and the headlight and wiper door actuators are plumbed out of it, right? So if I hook up the PCV valve to that large vacuum line, it won't effect how the engine runs? If I take the cap off that front port the engine dies, so the PCV valve must hold a vacuum, right?

Thanks for the responses!
-=Boston!=-

 

Uh -- NO. That is a charcoal filter. The idea is that all the fumes from the fuel tank and carburetor vent line are drawn into the charcoal canister by the vacuum coming from the intake. The fumes are then drawn into the intake for burning or are filtered by the charcoal.

The vacuum tank is in the front of the car. Your wipers and headlights should not be hooked to the evap. canister. They should be hooked to a vacuum source with a filter and a check valve.

It sounds like the entire vacuum / emissions set up on your car is less than correct. You may want to see if someone can post a diagram of the correct routing. Another method would be to purchase a vacuum and emissions hose replacement kit from Dr. Rebuild. Those kits come with the correct hoses, filters, check valves and diagrams on how to route everything correctly.


The PCV is a spring loaded check valve. It will draw in oil fumes from the crankcase area when there is a vacuum heavy enough to keep the valve open. You should remove that black plastic cap and run a line from there to your PVC valve. The engine should stay running when this is correctly connected. Do the connections when the engine is off or it will stall and die while you are moving hoses around.