PCV 2 post/port. Why?

[MadMax_636]

Im asking why the PCV vale has 2 ports on it. A larger (Bottom) smaller (Top) port. I know the larger port hooks right up to the PCV port on the carb but I dont know why it has a second port. I hooked a vacuum gauge to it while the truck was running and it pulls VERY little vacuum at idle but Ive always had it capped off. All of the replacements back both.

 

[Dirtman]

One port is for the evap system. The canister purges into the intake through the second port on the pcv valve.

 

[MadMax_636]

One port is for the evap system.

ok, So Im assuming for the original ignition system? With the duraspark system its unused.

I hooked it to the vacuum advanced port on my carb to see how it reacted. Since my dizzy's vacuum port doesnt work. (Ive been through 2 dizzys. The first one the vacuum gauge linkages failed and caused my timing to walk around and such. The second one the vacuum port doesnt work at all)

 

[Dirtman]

Had nothing to do with ignition, one port was direct to the intake for PCV vacuum and should run to the intake manifold itself or the carb below the throttle plate. The second port should connect to the charcoal canister, then another line from the charcoal canister should run to a ported vaccum port on the carb, above the throttle plate. When the engine is at a certain throttle position the second port will get vacuum and allow the charcoal canister to purge vapor into the intake through the pcv valve.

If you don't have that style of evap system you just plug one port on the pcv valve and run one to direct engine vacuum (below throttle plate).

 

[MadMax_636]

Had nothing to do with ignition, one port was direct to the intake for PCV vacuum and should run to the intake manifold itself or the carb below the throttle plate. The second port should connect to the charcoal canister, then another line from the charcoal canister should run to a ported vaccum port on the carb, above the throttle plate. When the engine is at a certain throttle position the second port will get vacuum and allow the charcoal canister to purge vapor into the intake through the pcv valve.

If you don't have that style of evap system you just plug one port on the pcv valve and run one to direct engine vacuum (below throttle plate).

When I said ignition system. I mean the emissions crap. I dont have any of the original emission stuff. So no charcoal can. 100% stripped down.

 

[Dirtman]

When I said ignition system. I mean the emissions crap. I dont have any of the original emission stuff. So no charcoal can. 100% stripped down.

Yea then just plug off the extra port and your good to go.

 

[MadMax_636]

Yea then just plug off the extra port and your good to go.

Just curious. Would it be good or bad to have that second port hooked up the vacuum advance port? Since I dont have vac advanced?

 

[Dirtman]

Im a lil rusty on my carb tech lol. If the vacuum advance port is direct vacuum then it wouldn't have any effect good or bad. If the vacuum advance port is not direct vacuum, meaning its above the throttle plate then no you should NOT hook it to that. PCV needs direct vacuum, if you connected one line to a direct port and one to a non direct port you'd basically just be creating a leak in the system and the pcv wouldn't function correctly.

You really just need the one large hose going to a direct vacuum source. Usually it's just run off the same place the brake booster is.

 

[MadMax_636]

Im a lil rusty on my carb tech lol. If the vacuum advance port is direct vacuum then it wouldn't have any effect good or bad. If the vacuum advance port is not direct vacuum, meaning its above the throttle plate then no you should NOT hook it to that. PCV needs direct vacuum, if you connected one line to a direct port and one to a non direct port you'd basically just be creating a leak in the system and the pcv wouldn't function correctly.

You really just need the one large hose going to a direct vacuum source. Usually it's just run off the same place the brake booster is.

Thanks! Yeah, the PCV port on the back of the carb 2150 (I should have stated that before) has a part on the back driver's side for the PCV system. The vacuum advanced (Ported vacuum) is on the passenger side. Long story short. All of my vacuum stuff is connected directly to the carb. Nothing below it.

 

[Dirtman]

Thats fine you just need to be aware that not all the ports on the carb give the same type of vacuum, that was the main point I was trying to make. In a nutshell the ports higher on the carb get more vacuum at full throttle, the ports lower down get more vacuum at idle. PCV needs the latter.

 

[MadMax_636]

Thats fine you just need to be aware that not all the ports on the carb give the same type of vacuum, that was the main point I was trying to make. In a nutshell the ports higher on the carb get more vacuum at full throttle, the ports lower down get more vacuum at idle. PCV needs the latter.

Thanks!

 

[AndyB.]

The original PCV valve from the factory only had the large port, unfortunately that was never available as a service part from Ford. The Ford service part D9BZ-6A666-A was carried forward from the ‘70s for this application. It came as a kit to cover multiple applications. The aftermarket manufacturers followed suit.