pcv making idle rough?

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gniknayrb18

gniknayrb18

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i changed out the intake manifold and the carb and pvc and now my car runs like..$#*!@...well kept messing with it and took the vacuum hose off the pcv and it runs great????what is going on
 
gniknayrb18 said:
i changed out the intake manifold and the carb and pvc and now my car runs like..$#*!@...well kept messing with it and took the vacuum hose off the pcv and it runs great????what is going on
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the pcv valve is prob bad and its just sucking air outta the valve cover. creating a vacuum leak. does the idle speed up when you hook up the valve? does is slow down when you plug the port on the carb?
 
Were the intakes exactly the same or was one used or cut? Sounds more like the intake swap created a vacuum leak rather than the PCV.
 
went from a holley street dominator to an eddy air gap and the idle speeds up when i take it off
 
if you have breathers on the valve covers you can delete the pcv valve and cap off the port on the carb. then adjust the carb idle screw accordingly.
 
i dont run one. car runs great.

found this right off the inter-web.

The blowby vapors that end up in an engine's crankcase contain moisture as well as combustion byproducts and unburned fuel vapors. The crankcase is sealed to prevent the escape of these gases into the atmosphere, but the vapors must be removed to prevent oil contamination that leads to sludge formation. The positive crankcase ventilation (PCV) system siphons these vapors from the crankcase and routes them into the intake manifold so they can be reburned in the engine.
The main component in the PCV system is the PCV valve, which is usually located in the valve cover. A hose connects the PCV valve to the intake manifold. A second hose between the air cleaner and crankcase or other valve cover (V6 or V8 applications) provides fresh air to help flush the vapors out of the crankcase. Some engines have a separate air filter for the PCV breather hose located inside the air cleaner.
The PCV valve is a spring-loaded valve with a specific orifice size designed to restrict the amount of air that's siphoned from the crankcase into the intake manifold. This is necessary because air drawn through the valve from the crankcase has a leaning effect on the fuel mixture much the same as a vacuum leak. So air flow through the valve must be controlled within certain limits. At idle, air flow is reduced because little blowby is produced. When the engine is cruising and vacuum is high, airflow through the PCV valve is at a maximum to purge the blowby vapors from the crankcase.
It's important to note that PCV valves are sized for specific engine applications. The wrong PCV valve for an application can flow too much or too little air causing driveability problems. Varnish deposits can clog the valve, so replacement for preventative maintenance is recommended (every 50,000 miles usually).
Not all engines have PCV valves. Some (like Ford Escort, GM FWD cars with the Quad Four engine, etc.) ventilate the crankcase with a small breather hose and calibrated orifice. There is no spring-loaded PCV valve. On these applications, no maintenance is usually necessary.
 
ok pulled the pcv out and capped the port on the carb and still running the same if i uncap the carb runs at high idle any ideas
 
no, your PCV system sounds like it is OK. Your carb is so rich you are idling rough (thats why it speeds up and smooths out with the line disconnected and open). Is it possible you had a vacuum leak before and the carb was adjusted rich to compensate? You fixed the leak with the intake swap and now you are rich. How about the power valve?
 
If it runs better with it blocked off, reset the idle speed and mix screws for best idle and find out why the PCV is causing you issues. It's nothing more than a metered vacuum leak.

Not having any idea what you have for engine or initial timing, no telling what the root isuue is.

Ede carbs are very sensitive to fuel pressure, too much pressure more than 5 psi, will mess you up.
 
no it runs better uncapped.....not hooked up to anything....put the pcv valve on and it idles rough...give it gas and it runs worse and dies
 
Ede carb? Look down carb throats when it's idling, if you see fuel dripping from the boosters, you have other problems.

Even if it's another brand, look down throats for dripping.

You should not see any fuel dripping.
 
Did you have the distributor out when you changed the intake?
 
crackedback said:
If it runs better with it blocked off, reset the idle speed and mix screws for best idle and find out why the PCV is causing you issues. It's nothing more than a metered vacuum leak.

Not having any idea what you have for engine or initial timing, no telling what the root isuue is.

Ede carbs are very sensitive to fuel pressure, too much pressure more than 5 psi, will mess you up.
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2x - but find and address the PCV issue. If it has to perform street duties, I always run a PCV system. Sometimes you have to play with the PCV valves to get one that works right - but that's what happens when you change engine components to non-factory stuff. But from what you're describing - you created a larger unmetered vacuum leak and you need to address that.

Also - stating the type of intake means little. Were they both new out of the box? Swap meet finds? Pulled off a friend's race car? In other words - did the 2nd intake fit properly? if you had to pry the intake to start the bolts, or had issues starting the bolts because the threaded holes were not centered in the intake's holes - then the intake doesn't fit properly.
 
it was a brand new intake and it went on pretty simple i pulled off an aftermarket intake as well so idk....gonna have a guy look at it later this week i adjusted the fuel air ratio screws and its running a little better just not right
 
i think i read somewhere i an take a can of staring fluid and spray around the carb and intake to check for leaks....is that true??
 
I wouldn't use starting fluid!
Use something like carb cleaner or brake cleaner with the long thin tube on the nozzle and be very slow and careful as they are very flamable. Spray in small bursts along the intake port top seems and around the base of the carb. Any change in idle speed or quality means there's a leak at that spot. Don;t spray heavy as it can also evaporate and get sucked into the carb - which has the same affect.

If the bolts all started easy in the holes it's probably fine but I'd test to be sure. Also - you will always have to adjust the carburetor for any changes in the engine - or somethimes because of the weather... so don't be afraid to have to touch something.
 
I think he says it runs better when the PCV port is left open. That would suggest it's really rich.

Good luck on it.
 
The choke should be completely pulled off if the engine is running temp.
 
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