The PCV valve has a spring in it so it stays closed at idle and does not dillute the a/f mixture at idle. So at idle if i pinch the hose shut with my fingers it shouldnt have any affect on idle speed correct? But it does. I cannot make my engine idle under 900 rpm no matter how far out I back the idle rpm screw. Only if I pinch the PCV valve line with my fingers. It is a brand new valve just bought it couple days ago. Tested the spring myself with a small screw driver. How much vaccuum should I have at idle. I have a vaccuum gage ill go check what I have. please advise Gary
Assuming your engnie is bone stock and it is in reasonably state of tune, I'd like to see 19-21 inches of Mercury (in/Hg). The reading should also be steady.
So when you pinch the PCV valve hose, the idle drops lower? That tells me that you might have a vaccum leak.
I believe that's how its suppose to work, During acceleration the vacuum drops that's when the pcv closes, when you need the extra air and fuel, then when you reach your cruising speed the vacuum increases and the pcv opens up again.
I agree with Jason;sounds to me it's a vacuum leak too. Or your carburetor is set too lean affecting the PCV vacuum signal.
no the PCV is supposed to stay closed when the vaccuum at idle when the vaccuum is highest, its when vaccuum falls off that it opens and lets the carb suck up the crankcase fumes... I think my vaccuum is low because my timing is retarded...
Pinching the hose closed will lower the idle. That is normal. The carburetor is calibrated for the small amount of air allowed by the PCV valve at idle. See where your idle vacuum is. It should be 20" with a stock engine.
when I pinch the PCV valve shut, then it will idle slowly. But if I dont pinch it, it cant go lower than 900. Wierd.
The PCV has nothing to do with it. You have something else going on. What's your idle vacuum in Park, fully warmed up??
vaccuum is 17 initial advance is 10 does it really make a difference if I set the advance in park or in drive? What rpm does the mechanical advance start coming in ?
And whats the vacuum reading with the hose pinched? Is the vacuum reading steady or is the needle fluttering?
It will tell you in the chassis manual. Ignition section. That is assuming you have the original distributor in the engine. 17" is low for a stock engine.
maybe the vaccum is low like you said and thats why it cant hold the PCV valve closed at idle so it is like a big vaccuum leak? the engine is stock with 40k miles on it
Nope. The PCV is not supposed to be closed at idle. You have a vacuum leak somewhere. Check the carburetor to intake manifold gasket. Pinch off the brake booster hose. See if vacuum changes.
Ill check those things tomorrow. Maybe it is the carb base. It does idle nice and slow when I plug the PCV hose FWIW. Not particularly smooth though. AT 900 its darn smooth. Going into gear is a small event though. ... Ill check leaks tomorrow. .. thanks for the tips much appreciated.
