What do I do next

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FlDart360

FlDart360

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Ok I finally took the advice of those on this form and added a PCV valve back to my engine. The PO just had a breather on each valve cover. The carb is a Holley 670/4150 the motor is a very mildly cam 360 that is ok with pump gas. When I connected everything up now my idle has jumped from 850 to 1000. Before I start turning screws and messing things up I thought should ask what caused this. My throttle stop screw is only about one full turn off the stop and my idle mix screws are both about 1 ¾ out.


I hope by the time I get off work today there might be some idea as to what’s going on here thanks. Don't mean to post and run but this is bugging me.
 
A pcv is a pretty big vacuum leak by design. PCV on one cover, breather on the other. The PCV should be hooked to the base of the carb and not the intake.
 
FlDart360 said:
Ok I finally took the advice of those on this form and added a PCV valve back to my engine. The PO just had a breather on each valve cover. The carb is a Holley 670/4150 the motor is a very mildly cam 360 that is ok with pump gas. When I connected everything up now my idle has jumped from 850 to 1000. Before I start turning screws and messing things up I thought should ask what caused this. My throttle stop screw is only about one full turn off the stop and my idle mix screws are both about 1 ¾ out.


I hope by the time I get off work today there might be some idea as to what’s going on here thanks. Don't mean to post and run but this is bugging me.
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PCV's add a little air/crank case mist by design as mentioned, so adjusting the idle down again is normal procedure.
Basically it just raises your idle a little and changes the idle AFR a little leaner at the same time. (pretty much just like opening the carb butterfly's a little more does, but without adding more fuel with it)
If you are picky about your idle AFR you can readjust that also.
It's ALL worth it to have the crankcase venting.
 
Donnie514 said:
Post #2 and #3 are correct. Need not say more.
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.........Except don't get hung up on what some "book" says about where idle screws should be. The throttle blade needs to be in the transfer slot (check your timing initial/ advance curve) Some older AFB / other carbs DID adjust idle speed by adjusting a vacuum leak--great big screw in the middle was simply an adjustable leak
 
What PCV valve do you have? Stock type PCV valves have 2 flow settings; a high flow setting for cruising and a low flow setting for idle. The change from one setting to another is based on the intake manifold vacuum. The high vacuum levels seen at idle in a stock engine 'switches' the PCV valve to the low flow setting so you do not get too much extra air into the engine at idle.

If you have a cam in the engine, your idle vacuum levels will be lower than stock. With a stock type Mopar PCV, those low vacuum levels will usually switch the PCV to the high flow setting; it is probably at the high flow setting at idle and dumping excess air into the intake. You need a different PCV in that situation.

Measure your idle vacuum level in the intake and let us know; stock Mopar PCV's switch flow rate at around 14-15 inches. Then a better PCV can be selected.

Some adjustment will be needed as said when adding a PCV. Also be aware that there is a secondary stop screw that sets airflow past the closed secondary butterflies that also admits air into the intake.
 
TrailBeast said:
PCV's add a little air/crank case mist by design as mentioned, so adjusting the idle down again is normal procedure.
Basically it just raises your idle a little and changes the idle AFR a little leaner at the same time. (pretty much just like opening the carb butterfly's a little more does, but without adding more fuel with it)
If you are picky about your idle AFR you can readjust that also.
It's ALL worth it to have the crankcase venting.
Click to expand...
Thank you... you confirmed what i thought might be going on, but i like to ask those that have been at this a lot longer than me.
 
nm9stheham said:
What PCV valve do you have? Stock type PCV valves have 2 flow settings; a high flow setting for cruising and a low flow setting for idle. The change from one setting to another is based on the intake manifold vacuum. The high vacuum levels seen at idle in a stock engine 'switches' the PCV valve to the low flow setting so you do not get too much extra air into the engine at idle.

If you have a cam in the engine, your idle vacuum levels will be lower than stock. With a stock type Mopar PCV, those low vacuum levels will usually switch the PCV to the high flow setting; it is probably at the high flow setting at idle and dumping excess air into the intake. You need a different PCV in that situation.

Measure your idle vacuum level in the intake and let us know; stock Mopar PCV's switch flow rate at around 14-15 inches. Then a better PCV can be selected.

Some adjustment will be needed as said when adding a PCV. Also be aware that there is a secondary stop screw that sets airflow past the closed secondary butterflies that also admits air into the intake.
Click to expand...

Image-1.jpg
 
Just make sure your primary throttle blades are covering only half the transfer slot. You may also have to refine the distributor. (It’s possible....)

Make sure when you reply, it is above or below the “QUOTE” tags!
 
rumblefish360 said:
Just make sure your primary throttle blades are covering only half the transfer slot. You may also have to refine the distributor. (It’s possible....)

Make sure when you reply, it is above or below the “QUOTE” tags!
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Will do. Probably should get some training from my kids their the masters of everything online related.:lol:
 
FlDart360 said:
View attachment 1715378509
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I looked at the Edelbrock site and there is no info on the vacuum level at which this PCV switches from high flow to low flow, or any info on how big the flow areas are. So you don't really know what you have there; it could be dumping all sorts of air into the engine.

What is the size hole in the grommet in the valve cover for this PCV? Just seeing if the size is such that you could easily pop in a better known PCV.

Also, can you measure the vacuum level in the intake at idle?
 
What size cam will require a pcv change. In other words, what generally is the largest cam you can run in a small block and keep a stock pcv?
 
Depends on the PCV and the state of tune. But generally, the stock Mopar PCV's will change flow if the intake vacuum drops below 14-15 inches. That does not take a lot of cam.... the ubiquitous 268 size cam will drop the intake vacuum that low, even with a good tune; 262's would probably drop the idle vacuum almost that low too.

Different PCV's are not hard to get; there is an MP PCV that switches flow at a lower vacuum level, as well as several others like Fram FV184; that unit was for mildly cammed factory GM V-8's. It fits a larger grommet size.
 
nm9stheham said:
I looked at the Edelbrock site and there is no info on the vacuum level at which this PCV switches from high flow to low flow, or any info on how big the flow areas are. So you don't really know what you have there; it could be dumping all sorts of air into the engine.

What is the size hole in the grommet in the valve cover for this PCV? Just seeing if the size is such that you could easily pop in a better known PCV.

Also, can you measure the vacuum level in the intake at idle?
Click to expand...


After reading your reply I realized I probably should have researched this a little better instead of just buying something that matched my valve covers. I was not aware of the different flow rates that a PCV valve can produce. This weekend I hope to get under the hood and take a vacuum reading along with trying what has been suggested. I too looked on Edelbrocks website and found no specifications on the unit. I will also measure the hole in the cover to provide more feedback. Thanks.
 
They are not all the same! Finding the one correct for you can be trying. Not sure I have a method per say but seat of the pants.
 
When close I think my idle will change by 1k or less much less. I have not done this in while and kept the card the last one came in for reference. Once you get there readjust idle and mix and record what you did. Have you considered a factory steel one!? I could not find one on resto and used a FRAM piece. I have grommets for all to use with factory covers.
 
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You will know when it is right, no blow out the breather and easily adjusted idle and mix! Nice clean engine with no fuss.
 
How about that one from Air Flow Research. I wonder if that would work?
 
TF360 said:
What size cam will require a pcv change. In other words, what generally is the largest cam you can run in a small block and keep a stock pcv?
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IDK the answer to that
but I ran a 292/292/108 on some crusty thing I had just laying around, probably off a smogger-teen. That's about the biggest cam you might run on a typical streeter. I ran that same used PCV on the next and the next and it now has over 125,000 miles on it. Ran it on my winter motor too, a stock long-block,1973, smogger-teen, with a TQ and TTIs.
IMHO, between [email protected] (the teener cam) and at least [email protected] (the 292/108); it don't matter; it will all work out in the T-port sync. Ok let me rephrase that; for me it made no difference. I've even run two of them on one particular combo,lol.
 
Update I was only able to get about an hour of test and tune time this weekend thanks to our daily weather washout and way to mush time spent on trying to get the yardwork under control. I grew up in this state and I have to say this has been a brutal summer so far and we still need to get past hurricane season.

Ok I took a vacuum reading at idle 17-18 inches this was before I took the next step which was to take a ½ turn out of the idle adjustment screw. Now with the engine warmed up and in gear I am now at 750 rpm or so. I still need to give it a good road-test to see if she has gone lean on me now.
 
nm9stheham said:
I looked at the Edelbrock site and there is no info on the vacuum level at which this PCV switches from high flow to low flow, or any info on how big the flow areas are. So you don't really know what you have there; it could be dumping all sorts of air into the engine.

What is the size hole in the grommet in the valve cover for this PCV? Just seeing if the size is such that you could easily pop in a better known PCV.

Also, can you measure the vacuum level in the intake at idle?
Click to expand...


17-18 Inches at idle.
 
TrailBeast said:
PCV's add a little air/crank case mist by design as mentioned, so adjusting the idle down again is normal procedure.
Basically it just raises your idle a little and changes the idle AFR a little leaner at the same time. (pretty much just like opening the carb butterfly's a little more does, but without adding more fuel with it)
If you are picky about your idle AFR you can readjust that also.
It's ALL worth it to have the crankcase venting.
Click to expand...


My follow up took a ½ turn out of the idle adjustment screw. Now with the engine warmed up and in gear I am now at 750 rpm or so. I still need to give it a good road-test to see if she has gone lean on me now.
 
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