PCV problems

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TAK65

TAK65

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Hi all,
another issue my handyman reminded me of...he could not adjust the idle low enough with the breather valve connected to the carb (1963 225 with a super six). With the hose hanging loose and the carb port capped, no problems. The valve was new/NOS one. Same thing with my all original 1964 Valiant w a 170 and original carb. Also a brand new valve. Can anyone shed some light on what we are missing here?
Thanks in advance,
Tina
 
Either you have something hanging up the throttle linkage / butterfly not allowing it to close, or you have a vacuum leak
 
Not all PCV valves are created equal. They are all basically calibrated vacuum leaks and some bypass more air than others. If you do have a vacuum leak as Del suggested it will be amplified when your PCV is connected. If no leak is found I would try a different brand of PCV or recheck application across a few manufacturers.
 
Possibly also, too much idle timing or vacuum advance engaged.

If it was a vacuum leak;
and since you have backed the curb idle screw out, and the transfers are rendered off,it should slow down with the PCV line working, and probably stall.
But if the throttle is hanging open, the transfers would still be operational, and the vacuum advance could be fully engaged,and then the rpm would be excessive.
If you had a vacuum leak at this time I doubt it would manifest, but using the PCV,the rpm would still change with it connected versus open line, versus blocked.
So in summary, I agree, likely the throttle is hanging open. Perhaps the fast idle cam, or the pedal linkage, or the tranny KD linkrod, or the carb base gasket.
 
AJ/FormS said:
Possibly also, too much idle timing or vacuum advance engaged.

If it was a vacuum leak;
and since you have backed the curb idle screw out, and the transfers are rendered off,it should slow down with the PCV line working, and probably stall.
But if the throttle is hanging open, the transfers would still be operational, and the vacuum advance could be fully engaged,and then the rpm would be excessive.
If you had a vacuum leak at this time I doubt it would manifest, but using the PCV,the rpm would still change with it connected versus open line, versus blocked.
So in summary, I agree, likely the throttle is hanging open. Perhaps the fast idle cam, or the pedal linkage, or the tranny KD linkrod, or the carb base gasket.
Click to expand...

Thank you all for your input. Anyway, as the rpm CAN be adjusted in factory settings when pcv is disconnected, I don't think the throttle could be hung open. Or can it?
 
If you make a plug with a hole drilled through it that can be inserted inside the hose for the PCV valve, you can restrict the volume of air passing through it. I've used small sockets and plastic plugs. Just be sure it will stay put in the hose.

Make sure all mechanical idle adjustments are set properly, verify that you have no other vacuum leaks by spraying carb or brake cleaner near the intake manifold flanges with no increase or decrease in RPM and make sure you sort out our ignition timing settings (note: virtually all Mopar engines like significantly more initial timing than stated by the factory, but you must reduce the timing added by the mechanical advance enough to keep the total advance at or below 32 degrees on a Slant 6. Vacuum advance disconnected during measurements)

Mine used to run best with 22 initial 32 total. It did have several modifications including large cam. Stock motors will like a bit less, but your motor will show you where to set it if you understand this process. Hook the vacuum advance to manifold vacuum. That way it will retard when the throttle is opened(heavy load), and advance when the throttle is near the closed or cruise position( light load).
 
It sounds like the PCV is just leaking too much air at idle. All PCV's should close down to a small amount of air flow when the vacuum goes high at idle. The stock OEM Mopar PCV's seem to need 16-18 inches of vacuum to close down.

So what idle vacuum do you have? Is this a modified engine? if the vacuum at idle is something like 15 inches or lower, then the PCV will not close down like it should, and it will provide excess air to the intake. If you have a cam in the engine, and the idle vacuum is in the 14 to 15 inch range or lower, then you can change to a different PCV valve that will close down to low airflow at a lower vacuum range. We used a Fram FV191 in my son's 340 for this exact problem.
 
What AJ said about vacuum advance could also have some input. IS your vacuum advance hooked up and if so to manifold or ported vacuum? Try it disconnected and plugged and see what that does. You may have carbon holding the PCV valve open at idle. Soak it with carb cleaner and whack it on the bench a few times and see what comes out. It may just need a good cleaning.
 
Talk-talk-talk-
Take the carb off, disable the choke, close the throttle, flip it upside down and look! If the throttle is closed it will not run unless it is sucking air AND fuel somewhere else.If it's not closed, make it so,and set the T-port sync.Set the mixture screws to 1.25 turns out from lightly seated.
Reinstall it. Hook up the return spring but nothing else. Make sure the choke is disconnected and it's cam is parked.Disconnect the vacuum advance unit and plug the carb port. Hook up the PCV correctly. Plug all other vacuum taps;on the carb, the intake, and, if you have a brake booster,clamp off the line.
Start it up. Set the timing to 10*. Then report back with an idle speed.
No more talking.
 
nm9stheham said:
It sounds like the PCV is just leaking too much air at idle. All PCV's should close down to a small amount of air flow when the vacuum goes high at idle. The stock OEM Mopar PCV's seem to need 16-18 inches of vacuum to close down.

So what idle vacuum do you have? Is this a modified engine? if the vacuum at idle is something like 15 inches or lower, then the PCV will not close down like it should, and it will provide excess air to the intake. If you have a cam in the engine, and the idle vacuum is in the 14 to 15 inch range or lower, then you can change to a different PCV valve that will close down to low airflow at a lower vacuum range. We used a Fram FV191 in my son's 340 for this exact problem.
Click to expand...

Does the Fram PVC fit a stock valve cover?
 
My vote is either an incorrect or malfunctioning PCV valve.
 
Thankyou everyone! Got a truckload of advice now, going to pass them on to the man. Hey, I'm just a girl :finga:
 
Did Maggie Thatcher ever say "I'm just a girl"? I think not! Git er Done!
 
340doc said:
Does the Fram PVC fit a stock valve cover?
Click to expand...
Not the stock stamped valve cover grommet; that is for a 1/2" OD PCV like the small diameter Mopar OEM part..... the metal one with the smooth 90 degree bend in the tube . The FV191 diameter is bigger than But you may be able to search around and find one that will fit the 1/2" hole (find one for a V8 GM car with a performance cam), or I think there are grommets for the later valve covers that can be found that will take a 3/4" diameter PCV like the FV191.

I found that the FV191 closed down properly at idle at 14" vacuum and flows more than the OEM Mopar part at low to moderate vacuum levels like at cruise or heavy throttle.
 
nm9stheham said:
Not the stock stamped valve cover grommet; that is for a 1/2" OD PCV like the small diameter Mopar OEM part..... the metal one with the smooth 90 degree bend in the tube . The FV191 diameter is bigger than But you may be able to search around and find one that will fit the 1/2" hole (find one for a V8 GM car with a performance cam), or I think there are grommets for the later valve covers that can be found that will take a 3/4" diameter PCV like the FV191.

I found that the FV191 closed down properly at idle at 14" vacuum and flows more than the OEM Mopar part at low to moderate vacuum levels like at cruise or heavy throttle.
Click to expand...

Thanks
 
Well worn carbs draw extra air through the side(s) where throttle rod goes through. Vacuum servos, at primary choke pull, and spark advance can leak too.
 
RedFish said:
Well worn carbs draw extra air through the side(s) where throttle rod goes through. Vacuum servos, at primary choke pull, and spark advance can leak too.
Click to expand...

Good point! If the throttle shaft has worn out the carb base then you need a new carb!
 
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