PCV Valve - What?

[XframeFX]

This would apply to all 60s and 70s engines. But I purchased Echlin PCV Valves for my Nailhead.

 

There's been some mention how important this valve is which I can only agree if in daily use with high mileage as the failure mode is a gummed-up valve limiting flow. I can't see how crankcase pressurization could ever occur. Maybe idle quality if plugged. For our classic rides, this will probably never happen with the few miles we Log.

Carburetor is designed for vacuum to flow through this valve.

 

PCV is simply a Check Valve and a crude valve at that.

I'm surprised NAPA Parts counter people weren't perplexed with me having them pull all their Echlin PCVs to test them in a row. They all leaked! Doesn't matter I assume.

 

However, I recall PCVs having a positive reverse block in my early days. Not so today.

 

Am I wrong unassuming failure mode is only a fouled valve blocking flow in either direction?

 

This is a Rockauto screen-shot. No Echlin valve shown:

[NTX5467]

Of all of the pcv valves on my vehicles, I have never had one to fail or get so completely gunked-up that it would not "clean" by flushing it with spray Berryman's B-12 carb cleaner.  In the few new ones I've bought, NO difference in performance.

 

Yes, the pcv is a variable vacuum bleed situation.  Little flow at high vacuum, more flow at low vacuum.  It should rattle, which is the main criteria I used to judge if they needed bi-directional cleaning.  Plugging one end with a finger, filling it with B-12 cleaner, plugging the other end with a different finger, then shaking it back and forth to move the plunger around.  Then drain and flush in both directions.  Usually not much needed before the cleaner came out clear.

 

There should be NO rubber in the valves to facilitate a tight seal between the plunger and the valve's body.  Hence what you found, machined surface against smooth metal or plastic surface.

 

Yes, there are flow ratings for the valves.  The ONLY place I've ever seen them was in a 1970s-era Exxon Tune-Up Manual, in the back.  In the realm of Chevy engines, the L82/LT-1/Gen I and II Z/28 engines had a higher-flow valve (had a purple dye on the metal/bottom portion) than the normal valves.  Apparently to help with the higher idle air requirements of the bigger-cam motors?  I tried both in my '77 Camaro 305 after I upgraded to a "more cam" situation, but could really not tell a significant difference in hot base idle speed.

 

The only thing that might fail in a pcv valve is the spring.  If it should break, there will still be some spring pressure to resist the valve closing all of the way, with the air passing through it being restricted more of the time.  Pretty fool-proof, it seems.

 

To me, the best valves to have would be the older OEM ones, cleaned, of course.  PCV is needed to decrease crankcase gunk and sludge from happening, especially in cold weather.  More reliable than the prior road draft tubes, which needed vehicle road speed to work well.

 

Only about 10 weeks to April 1st!

NTX5467

[RivNut]

Any recommendations for a screw in PCV valve for my ‘64?   I’m running two finned aluminum valve cover each of which has a twist in breather.  I also have a finned aluminum valley cover which will be machined, drilled and tapped for a screw in PCV valve, with a baffle under the valve so nothing can clog it.  I know that PCV valves are different for different types of engines.  Can anyone recommend what they would consider the correct valve for this 425 w/ ~ 70K miles on it? 
 

TIA,

Ed

[RivNut]

Here’s a picture of the valley cover ( lying upside down on a tire) from Dave’s car.  I’m doing the same thing, I just have no idea which PCV valve to use.

[Rockable]

@RivNut,If you're going to use that, you need some sort of baffle to deflect the oil that is slung from the camshaft lobes. Otherwise, it will suck up and consume more oil than you'd like. It wouldn't be hard to make one that is captured between the pcv and the valley pan. The older Nails had a baffle for the draft tubes.

[60FlatTop]

The doctor picked me up by the ankles and gave me a slap on the bottom to install my information that PCV valves bleed.

 

On the topic of Echlin parts, that is all I buy now. Standard and new stock Delco have let me down. Sometimes I will go for old stock Delco if it is early '70s on back.

Even as a faithful long time AC Delco spark plug user I have switched to NGK's.

 

Here are some comparison pictures between Echlin and Delco points that I took in 2011. It was not just a random thought to take the pictures. I was inspired by a flatbed ride.

 

The Echlin are the heavier better built ones.

[Lee H]

15 hours ago, RivNut said:

I just have no idea which PCV valve to use

You might want to investigate what I use on my ‘62. Wagner makes an adjustable valve, that can mimic the flow of any stock PC valve during high and low vacuum situations. At around 150k I was beginning to get some minor blowback from normal wear, that the stock PCV was unable to deal with effectively. After install and tuning, my firewall has been clean for four or more years now.

https://mewagner.com

 

[RivNut]

10 hours ago, Rockable said:

@RivNut,If you're going to use that, you need some sort of baffle to deflect the oil that is slung from the camshaft lobes. Otherwise, it will suck up and consume more oil than you'd like. It wouldn't be hard to make one that is captured between the pcv and the valley pan. The older Nails had a baffle for the draft tubes.

If you’ll look at the picture that I posted, you will see a baffle. 

[XframeFX]

9 hours ago, Lee H said:

You might want to investigate what I use on my ‘62.

Yes, thank-you Lee H. I did investigate after a previous recommendation by yourself. My thinking keeps defaulting to it being a Check Valve.

All those open boxes on the NAPA Parts Counter had PCV Valves behaving the the same. Correct after all?

 

A good starting point is that mewagner.com site, TX

 

BTW: It appears RivNut is looking for a physically compatible valve rather than questioning its operation.

Hopefully, can address both here.

 

[Rockable]

My bad. Looked at it on my phone.

Edited January 21 by Rockable (see edit history)

[EmTee]

Or, machine the valley cover to accept a '67 430 grommet and valve.

 

    

[RivNut]

These are too nice for grommet and an ugly hose sticking out of one of them.  😊

[NTX5467]

The first Chevy pcv valves were screw-in, circa 1964 or 1965.   The "attachment" to the block replaced the prior road draft tube at the back.  One longer screw held it in place.  Then a rubber hose between that item and the screw-in pcv valve on a fitting for the rear of the carburetor.  Probably can find them in the Corvette or Impala repro websites?

 

NTX5467

[RivNut]

There are a number of screw in PCV vale’s out there. Currently most are used in Asian built cars.  In 1967, the 302 high performance Chevy in the Camaro used one.  My problem is trying to figure out which configuration the nailhead needs.  The one for the 302 is designed for a high RPM small block.  Different configurations - big block vs small block, high RPMs vs low RPMs, what kind of pressures are built up within the block.  These are the situations that I need to take into consideration when choosing the correct valve.

[EmTee]

2 hours ago, RivNut said:

hese are too nice for grommet and an ugly hose sticking out of one of them.  😊

I agree, however, I was talking about the rear of the valley cover which wouldn't be visible standing in front of the engine.

[RivNut]

27 minutes ago, EmTee said:

I agree, however, I was talking about the rear of the valley cover which wouldn't be visible standing in front of the engine.

If you’ll look back at the picture of the upside down valley cover that I posted earlier, you’ll see that this PCV valve is threaded into a hole in the back of that cover.  My plans call for the shortest, most inconspicuous hose possible.

[Bloo]

On 1/20/2024 at 3:02 PM, RivNut said:

If you’ll look at the picture that I posted, you will see a baffle. 

That's a good start. I have a strong hunch you are going to need a lot more elaborate baffle than that. If the baffle is inadequate, your oil consumption will skyrocket. There is probably less oil spraying around in there than say... a valve cover, but still, Chevrolet had an elaborate oil separator down in the valley for the draft tube and just kept using it for a couple of years when PCV came along. You need to separate the oil from crankcase vapor, otherwise you will just burn it. Watch your oil level like a hawk until you figure out whether your solution was adequate.

 

3 hours ago, RivNut said:

There are a number of screw in PCV vale’s out there. Currently most are used in Asian built cars.  In 1967, the 302 high performance Chevy in the Camaro used one.  My problem is trying to figure out which configuration the nailhead needs.  The one for the 302 is designed for a high RPM small block.  Different configurations - big block vs small block, high RPMs vs low RPMs, what kind of pressures are built up within the block.  These are the situations that I need to take into consideration when choosing the correct valve.

Choose a valve for an engine of about the same displacement and RPM range. That's the easy way. It's about flow. Theoretically one from a smaller but higher RPM engine, or a larger but lower RPM engine could possibly be fine, but there is too much to think about. Just hit the displacement and redline in sort of broad strokes and try it. If it's too much, go smaller.

 

You will never match what the nailhead or any other engine "needs". Even with careful carburetor recalibration, there is a limit to how much of a parasitic vacuum leak an engine will tolerate. It is *never* enough air to ventilate the engine 100% of the time. On a brand new engine, some percentage of the time the PCV system will blow backwards. This is why there is always a little slime around a breather cap. As the engine wears and blowby increases, the amount of time the PCV system can keep up decreases, sometimes dramatically.

 

Pay attention to the direction of flow. It's not always obvious. It helps if you can see a valve you might use installed on the car it belongs on so you can be sure which way it goes. Threads don't mean much.

 

On 1/20/2024 at 7:13 PM, XframeFX said:

BTW: It appears RivNut is looking for a physically compatible valve rather than questioning its operation.

Hopefully, can address both here.

It's a check valve, and also flow metering. Without a check valve, a backfire can cause a crankcase explosion. Also, early systems that used an orifice instead of a PCV valve plugged the orifice very quickly. The PCV valve prevents plugging, not perfectly, but it is a huge improvement over an orifice.

2 hours ago, RivNut said:

 My plans call for the shortest, most inconspicuous hose possible.

For PCV to work correctly, The carburetor needs to have a dedicated PCV port, or you need a dedicated PCV plate under the carburetor. Some carburetors have the PCV routed out the back, but not many because the idle jets are in the front. You'd need one of those with PCV on the back for maximum stealth.

 

The PCV vapors need to mix with the incoming air/fuel or you are gonna have a bad time. Most commonly, the ports exit right below the idle jets. Some Fords had it over closer to the axis of the primary throttle shaft, but the goal is the same. It must mix with whatever is coming through the idle jets and transfer ports. Any PCV passage you make will have a tendency to plug right away, and you will notice the passages in carburetors and OEM PCV plates are huge. The outlets where they mix with the air/fuel are also huge. It's no accident. All flow metering is done at the PCV valve (or orifice). Plain vacuum ports will not work. It has been done, A few Ramblers and some circa 63 "California conversions" are like this. No amount of rejetting or recalibration can fix it, even if you don't mind how much fuel you burn. The fuel distribution is just too far off. Cars like this are basically untunable, and stink to high heaven.

 

One final thought. There has to be a way in for fresh air (a breather cap will do), but if there is still a draft tube in the mix somewhere it must go. It becomes an inlet, and will suck dirt during the periods the PCV works. Best of luck picking out an appropriate valve.

 

[Wayne R]

Hello Ed , just incase  you could do the opposite and show it---like this for sale on

ebay   item number 263351479654.----could be to big.

[NTX5467]

When I looked in the 1946-1972 Buick Parts Manual, it listed only ONE pcv valve for 1963-1971 All V-8s.

6478503, which replaces 6421972

Looking in Rock Auto for 1963 Riviera 401 . . . ACDelco 19310783    Looks like it is designed to plug into a grommet on the LH valve cover, two different size end fittings.  RA showed grommets for such.

 

For 1965 Corvette 396:  Standard Motor Parts V100, which is a screw-iin valve with a hose attachment on the other end.  No sizes listed as to fitting it screws into or the hose size that attaches to it.

 

These items are listed in Group 1.745 of the GM/Buick parts book.  Probably have to find a '63 or so factory service manual which can detail the crankcase vent system.  Similar for a 1965 Corvette parts book, but I recall the illustration of the early pcv system in a 1972 printing of the Chevy car parts book.  The "Ventilator" (which fits in the lifter valley) and attaches to the road draft tube, for the closed crankcase vent systems, the road draft tube is replaced with a cap (with a bolt going through it to the anchor for the road draft tube and bracket, plus a seal under the bolt head), with a nipple on the cap to which a rubber hose attaches that goes to the valve, which screws into a brass fitting that screws into the rear throttle body of the carburetor.  Or an inline valve with hose attachments on both ends.  THESE would be the things to look at in the Corvette repro vendor catalogs.  A simple system to adapt to an older car, it seems to me.

 

Enjoy!

NTX5467  

[NTX5467]

I went in search of a parts diagram of the pcv system.  First on a '65 Corvette 396 and then on a '65 Impala 327.  The 327 V-8 was the item I remembered, but it was a little bit different.  There was the metal tube which attached to the road draft tube location, but that was the INTAKE for the air, so the rubber hose went to the air cleaner base.  The pcv valve screwed into a bung on the front oil filler tube, with a hose going to the carburetor base.  Basically reversing the direction of air flow into the engine.

 

There are also some oil filler/sealed breather caps which have a nipple on them.  Those could be adapted to use an inline pcv valve situation, I suspect.  Most are chrome, if that matters.

 

NTX5467

Edited January 22 by NTX5467 (see edit history)

[Lee H]

13 hours ago, RivNut said:

These are too nice for grommet and an ugly hose sticking out of one of them.  😊

I agree! But I will say this: the most effective ventilation system pulls fresh filtered air in from one valve cover with the PCV suction in the other. Eventually, this is the flow pattern all the manufacturers adopted. Lincoln went with PCV early on the 430, in 1961 (probably more to avoid the possibility of customers smelling crankcase fumes, than an engine longevity strategy), but they really only re-purposed the road draft tube mount in the valley pan, so under the valve covers, the vapors are stagnant, and it always looks bad under there when even you pull one. Here is how Ford evolved from the early to the late 60’s.

[XframeFX]

18 hours ago, Bloo said:

No amount of rejetting or recalibration can fix it, even if you don't mind how much fuel you burn. The fuel distribution is just too far off. Cars like this are basically untunable, and stink to high heaven.

This is hitting close to home.

I blocked power brake vacuum source during past tuning/trouble-shooting. I should've blocked the PCV hose as well. Nothing I do to the carburetor seems to accomplish much.

 

I was relying on correct replacement parts such as using process of elimination for the PCV Valve. However, I have learned "meets or exceeds" is not correct at all. More like "one part fits all", a Chevy part.

 

 

 

Edited January 22 by XframeFX (see edit history)

[NTX5467]

Over the years, I have run into situations were the carburetor became insensitive to whatever I did to it.  Mainly on idle screw sensitivity in adjusting them.  One side works and the other one did not.  Disassembly found nothing more than a clogged pcv circuit in the carb base plate.  Clearing it out did not help the situation.  So, a new carburetor was sourced and things were good again.

 

BUT, it seems that the "window" for OEM calibrations is a bit small, as the window for "Works Dang Good" being much wider.  To me, as long as the spark plugs burn "in the window" of "good", the main system mixture is not too rich to deliver good highway fuel economy, and the idle can be set to work well (mixture and hot base idle speed), then you are near the top of the "works well" window.  Even with aftermarket parts.

 

As to the "smell", if the smell is not from excess fuel (which should be blackening the spark plug terminals and possibly putting similar smells in the motor oil), then I highly suspect it is a "Fuel Issue".  One day, back in the middle 1980s, I was driving around one Saturday afternoon in the metro area and bought gas from a Ci___ station (new to this region at the time, which had a refinery in Louisiana at the time).  No big deal, but as the day progressed, I noticed that I needed to throttle into the engine to get the car to idle in gear at traffic lights.  On revving it, the exhaust has a hollow sound to it.  It took a bit longer to start when cold, but still ran with some help.  The closer I got to Empty, the worse it seemed to get, so I went on a mission to get to "E" sooner than later.  New gas fixed it.  Last time I bought that brand of gas.  A few years later, that brand vanished from the region, for one reason or another.

 

Used to be that each major brand of gas had their own tank truck fleets to deliver was from THEIR tank farms to THEIR dealers.  That distribution model has ceased to exist, it seems.  Generic gas arrives at a distribution point.  As it is loaded into the tank truck, the defining additives and such (for each brand) is added to the batch at that time, "Splash blended".  Not unlike the middle 1960s when generic gasoline was loaded and the additives the customer desired was added at that time, "blended" on the way to the customer.  BTAIM

 

I FULLY agree with @carbkingon OEM calibrations being the best, BUT they were also designed around gasoline that was leaded and "more real" than what we have now.  Designed for carburetor use rather than EFI, too.  Much less consideration of 10-15% ethanol!  Especially the ethanol to the amount we now have!!!

 

OEMs have much greater instrumentation of their emissions work projects, then as now.  Unfortunately, to get to some of those "numbers" is one thing, as numbers a little bit more to the "rich" side of things will not be felt, but only indicated by "the instruments", typically.

 

I also have observed that with newer carburetors, the reaction to off-idle can be sharper than the OEM carbs could ever produce.  Even when using a newer OEM carb to replace an earlier one of a different manufacturer.  Some things DO get better, the "younger" they are, from my experiences.  In that respect, I'm not afraid to use a newer carb to replace an earlier one in an OEM application.  With the AVS2 being one of those situations.  Or a Street Demon to mix the best attributes of a square-bore and spread-bore carb in a package that will bolt onto anything 4bbl for many years.

 

When I happened onto that early-1970s Exxon Tune-Up Manual, with the flow rates of pcv valves listed by application, I was surprised how close they all were.  As to flow rates, there is an SAE Transaction which GM presented back in the early 1960s, where they installed a few different flow rate systems on a few of their security service cars, which were 1961 Chevy Biscayne (or BelAir) 235CID 6-cyl cars.  They had one with the draft tube, as produced OEM.  One with a low-flow rate system.  One with a system twice the flow as the low-flow system.  As the cars idled for long periods and always drove slowly, these were good guinea pigs for "worst case scenarios".  

 

The lower-flow system did better than the draft tube engine, as expected, decreasing sludge by a good bit.  The higher-flow system did even better than expected in keeping the crankcase clean.  Proving the benefits of having a pcv system on the engine.  Atr the time I found this in the Texas Tech University library, I was not specifically concerned with related carburetor calibrations on the systems.  Knowing that if any additional air would be needed to get to the hot base idle speed, that would be just a tweak away.  Same on any issues with idle mixture, too.  Nor did I later notice that carbs in the Holley Variable Spec Manual were rated for pcv systems or not, or different for years when pcv systems were factory installed.  Nor later when the CARB required the retro-fit of pcv systems to 1955-era vehicles.

 

To me, these things mean that a few minor tweaks to a carburetor can be made (idle speed screw, base timing) to accommodate a pcv system where one was not there OEM.

 

I also consider "factory specs" to be a starting point from which "optimum" tuning can be achieved.  Some engines are more responsive to such things than others, but "lean best idle" works for everything.  As some idle systems are much more sensitive to mixture screw adjustments at different idle rpm levels, for example.  Some "windows" are wider than others.

 

Whenever adding a new/different carburetor, always look at the factory jetting specs for the main and secondary systems.  Compare and then see how the new carb works before changing anything.  You might discover the new carb's calibrations are pretty close to the OEM calibration.  Unfortunately, there are other "hidden" calibrations in the venturi cluster or metering blocks that we do not know about or how to change, in some cases.  Making the jetting a "rough comparison" of sorts.

 

In the mean time, hope for an earlier Spring season so you can get our and drive the cars!

 

From my experiences and observations,

NTX5467

Edited January 23 by NTX5467 (see edit history)

[XframeFX]

On 1/22/2024 at 5:26 AM, Lee H said:

the most effective ventilation system pulls fresh filtered air in from one valve cover with the PCV suction in the other.

Tested this with a square piece of yellow post-it note (sticky side up) over the open breather/filler hole in earlier trouble-shooting. Also, blocked PCV momentarily with my thumb to observe idle quality and vacuum. It went from 15-16" to 17-18".

 

I think I need to plug the PCV and power brake ports then attempt tuning adjustments again. Success or not, re-connect and see where I'm at.

 

Like many replacement parts, I have zero trust in the various PCV Valves I have purchased for this engine.

 

No silver bullet!

[carbking]

Willis - a minor disagreement about newer carbs versus older original carbs.

 

If one has a 1965 Nova 327 with pop-ups, big cam, and headers, then I won't argue.

 

But for the vast majority of older carburetors, I think the biggest issue is not the carburetor, but the understanding of the carburetor by the individual working on the carburetor. (No offense meant to anyone, just my opinion).

 

Many carburetors have a "gotcha" (so do efi, its called sub-zero weather!). Starting an engine reliably in sub-zero weather is easier with a carburetor with a manual choke, and Mobil 1 (opinion).

 

But discussing three of the more common "modern" (1957~1975) carburetors most folks will encounter, the Carter AFB, the Rochester 4G(C), and the Rochester 4MV (Q-Jet). I have posted all of this before, but here getting it all in one spot.

 

The Carter AFB has sacrificial step-up pistons. The earliest AFB pistons were brass. About 2 months, and carb housings were wearing, causing an internal vacuum leak, and a rich condition at all engine load except wide open throttle. Carter recognized this fact, and quickly changed the material from brass to aluminum, AND the aluminum alloy used for the pistons is much softer than the alloy used for the carburetor body. Thus, the pistons will wear, but the housing does not. Since Carter was in the business of selling carburetors, I personally think this decision admirable. (Opinion) rebuilding a Carter AFB WITHOUT replacing the pistons is like throwing a rock at a mountain lion, just asking for problems.

 

In 1956 Rochester started using a spring-loaded air valve on many of their 4G(C) carburetors. Air valve springs fatigue. When the spring fatigues, the air valve will open too soon, causing a bog a.k.a. hesitation when the secondary side of the carburetor is engaged. Again, rebuilding one of these without replacing and adjusting the spring is about as fruitless as trying to win an argument with the IRS!

 

The Rochester 4MV a.k.a. Q-Jet can have several "gotchas", the earlier versions more than the later ones, as Rochester like Carter, recognized issues, and corrected them as they were identified. The 1965 4MV is probably best left to a carburetor professional. The 1966 version somewhat improved, the 1967 version even better, and by 1968 the 4MV was a really good carburetor, but still had issues. The internet is full of disturbed pixels about bushing the primary throttle shaft, so will leave that one alone, other than to comment that many folks would be better off taking the throttle body to a machine shop! But the 4MV, like the 4G(C) has a spring loaded air valve. Interestingly, the exact same spring! Replace it. But the hidden issue here is the plastic cam that controls the opening rate and final height of the air valve. A metal follower rubs on the plastic, and metal is generally harder than plastic. The plastic cam wears. And due to the geometry of the design (the cam is between the base and the rod) the lift reduction due to wear is double the wear. Always replace the cam and spring when rebuilding a 4MV.

 

Other carbs have their own gotchas. Some of these I understand, and some I didn't work on, so have less, or no, understanding.

 

Jon

[Bloo]

31 minutes ago, XframeFX said:

I think I need to plug the PCV and power brake ports then attempt tuning adjustments again. Success or not, re-connect and see where I'm at.

The power brake port should make zero difference. It only lets a booster can load of air in when you first touch the brakes, and since the engine is decelerating it does not care. If it makes a difference to the tuning, you have a leak down that vacuum line somewhere, probably a bad booster, and you need to fix that before proceeding.

 

The PCV port would be instructive, especially if you have added a PCV valve to a carburetor that did not have one somehow, but afterward you will have to retune with it hooked back up. It is a vacuum leak, and the only reason the engine tolerates it at all is the PCV ports in the carb or spacer plate that cause the incoming crankcase air to mix properly with the air/fuel coming from the idle jets and transfer ports.

 

In theory, adding PCV to a carburetor that never had it should always require some internal work, more than just readjusting the idle jets. Ive seen people get away with it though, and more often than I would expect. The key is mixing the PCV air below the idle jets like a factory system does. Since there is more air getting in that did not come through the carburetor, the throttle will need to be slightly further closed for the same idle speed, and the idle slightly richer. The transfer ports are not adjustable though. Transfer ports, along with the idle screw ports, are typically fed from fixed orifices. In theory you would have to make changes there. In practice, I have seen cases where those were already a little too rich and it just worked.

 

 

[edinmass]

I have always found it fascinating that was the clean air act kicked in, and all the pollution control garbage started getting installed on cars, you didn’t tune the car up to run its best. You didn’t tune the car up to get its best fuel mileage. You tuned the car, so it would pass emissions……. I remember in the 70s and 80s in the inspection bays adjusting the carbs by knocking out the plugs to make adjustments to the mixture screws. Once we got the car to pass emissions, we would then go to the customer and ask them if they would like us to tune it up…….. tuning a car to pass emissions was a totally different subject than tuning a car to make it run well. I clearly remember the faces of the people realizing that once the car passed the emissions test required in Massachusetts, you then needed to tune it so it would run right. Made a bunch of money going from tuned for a sticker to tuned for milage and performance. 

Edited January 24 by edinmass (see edit history)

[NTX5467]

@carbking, thanks for verifying a point of curiosity on the Carter aluminum power pistons.  I had always wondered about their wear and related vac loss through them, but figured a lighter spring under them would do the trick.  Yet the OEMs never did offer replacement springs, but they were in the Carter Strip Kits (for both the AFB/AVS and TQuad) and the later Edelbrock kits.

 

Regarding the QJet secondary cams . . . the Chevy parts book did not mention them anywhere, but I knew they were on the carburetors and could be a wear item.  As it turned out, some of the GM carlines had them in the parts illustrations with a ref number for them, which related to the parts list, but not consistently from model year to model year.  Never did find them in the parts lists in the Chevy parts book, though, unless they were hiding them somewhere else.  The OEM replacements were thinner than the production ones, too, as if they wanted them to wear.  Many techs did not know of their existence, either.

 

I remember when the primary throttle shaft wear issues surfaced and the first kits for DIY use (after the ones where a machine shop was needed).  I had noticed some such issues on older carburetors, at that time, but never worried about it unless it was "a lot".  In a Holley carb seminar I went to in the earlier 1980s, the Holley engineer claimed there should be some "looseness" in the shaft/throttle body interface.  Plus that such looseness was figured into the carb's metering characteristics.  As if "Don't worry about it.  If you do, we sell new throttle bodies."  Seems like Rochester sold new ones, too, but by the time they would be needed, they'd be "Obsolete" and/or "Discontinued" items.

 

Perhaps what is needed is for a dyno operator of repute, to test a stock Nailhead on the dyno, but only at hot base idle speeds.  With "a hat" on the carburetor to measure air flow into the carburetor.  Then do a comparison air flow check with the pcv valve open and compare it to when the pcv valve is closed, to determine just how much air flow goes through the valve when it is hooked up.  Maybe even test a clean OEM NOS valve against a newer replacement for the same application?  Checking and adjusting the air/fuel ratio at idle each time at the factory hot base idle speed.  Then see what idle mixture screw adjustment changes might be needed to maintain a 13.5 or so AFR?

 

A side issue might be that as most of the idle systems were oriented toward a smooooth idle, they would be richer than the later emissions settings.  Might be that the 1955 V-8 might automatically get a leaner idle setting, for lower emissions, as a result, too?

 

Things to find:  The SAE Transaction I mentioned on the GM testing and decision on their early pcv systems.  As to flow rates of what was tolerable.

     The earlier CARB test papers on their retro-fit systems and how they affected the vehicles they were installed onto.  As to which pcv valve applications they used.

      The comparison of carb main jetting on the pre-pcv carburetors and the pcv carburetors, for several applicable applications.

 

Thanks, @carbking for your input on the carburetor issues!

 

Y'all enjoy!

NTX5467

[carbking]

When did Buick start using the PCV?

 

Jon

 

[NTX5467]

In the research I just finished doing via Google, it appears the CA vehicles started to use them in 1960, with national use starting about 1963.  Many GM lines, as Pontiac, apparently phased them in in 1961 model year.  Not everybody at once, apparently, but voluntarily prior to the federal requirement  I know our '61 Chevy BelAir 6-cyl did not have one.

 

Fram FV112 and FV112DP, via the Fram website, indicates that part number to fit the vast majority of GM cars built between 1961 and 1975.  From 3.8L inline sixes to '75 455s.  Which tends to indicate two things . . . 1) that the flow needed to keep sludge accumulation (from short trips and such in cold weather) minimized is not necessarily engine displacement-related,  2) that the amount of flow related to engine size might not be as critical as suspected.  Which means that any flow is better than no flow.  Looks like the "big end" is the same hose size as the bolt-on fitting that went in place of the draft tube, too.  Which would then mean the "place of flow compensation" would be in the carburetor calibrations, YET none of the discussions I found mentioned carb issues after installation.

 

I found a good discussion in the CLC forum about 1955 Cadillacs, using a carb base spacer/gasket with a flattened tube going into it, which the pcv hose would attach to.  A mention of the MEWagner item mentioned in these forums recently.  Plus the amount of information on their website as to pcv valves and such.

 

I found one aftermarket kit which referenced a Fram pcv valve which fit 4.6L V-8s to 5.8L V-8s, in a Ford-related forum.

 

There was also a discussion about Tri-Five Chevy V-8s and adding pcv systems to them in H.A.M.B., noting the different length of the internal "ventilators" on particular model year V-8s and their interaction with factory and aftermarket intake manifolds.

 

Y'all enjoy!

NTX5467

[XframeFX]

5 hours ago, Bloo said:

The power brake port should make zero difference.

The vacuum accumulator vessel never seems to hold vacuum immediately after shutdown even after an expensive power booster rebuild which was returned to me painted black, not plated. Didn't even include a new external check valve. The 60 year old valve checks-out functional but don't trust it and yes, shouldn't make a difference. Only the power booster could have a leak if it even had one in the first place (before rebuild).

 

Carburetor is also an expensive trailer park rebuild with scuffed pistons re-installed. I swapped-in better used meter rod pistons and played with various springs ending with the originals back in.

The AFB has PCV port out the back over the secondaries. I have a Cadillac spacer with a PCV port out the front. However, primary bores are only 1-7/16" not 1-9/16".

Assuming my issue is the AFB idle circuit but Lean condition persists with primaries as well.

With the return of driving season, will bring nailhead to operating temp. Pull over to a safe roadside spot, install yet another set of new sparkplugs, block all vacuum assessories and make a little road trip (no idling) for sparkplug inspection.

 

That ME Wagner product might. Be in my Riviera's future.

[Bloo]

That AFB pcv port probably goes to the front barrels even if it physically comes out the back. I hope it does. I have seen some carbs that had PCV feeding over the secondaries, Chevrolets I think it was, with 4-jet or maybe WCFB. That can't possibly work well, and they changed their method right away.

 

If the power brakes leak, that is a big problem, rebuilt or not. They shouldn't leak, at all. You mention an accumulator vessel. Is this a separate tank? Check it for leaks. Make sure all hoses fit tight. They shouldn't have to get smaller with a clamp to hug the nipple. The hole in the hose should have to stretch a wee bit to go over the nipples. If it doesn't, get a smaller diameter hose. Clamp them to keep them from potentially falling off, but they shouldn't need clamps to seal.

 

On just about any of those old power brake systems you should have 2 good stabs of the brakes under power after you have shut the engine off.

 

Edited January 24 by Bloo (see edit history)

[Lee H]

12 hours ago, NTX5467 said:

The comparison of carb main jetting on the pre-pcv carburetors and the pcv carburetors, for several applicable applications.

For Lincoln, the Carter ABD used in 1961 (PCV) was jetted roughly 4% richer than in 1960 (non-PCV). While they were both 430’s, this may not be the best comparison because the 60 was a heavier car and slightly different gearing.

[1965rivgs]

15 hours ago, Bloo said:

The power brake port should make zero difference. It only lets a booster can load of air in when you first touch the brakes, and since the engine is decelerating it does not care. If it makes a difference to the tuning, you have a leak down that vacuum line somewhere, probably a bad booster, and you need to fix that before proceeding.

 

The PCV port would be instructive, especially if you have added a PCV valve to a carburetor that did not have one somehow, but afterward you will have to retune with it hooked back up. It is a vacuum leak, and the only reason the engine tolerates it at all is the PCV ports in the carb or spacer plate that cause the incoming crankcase air to mix properly with the air/fuel coming from the idle jets and transfer ports.

 

In theory, adding PCV to a carburetor that never had it should always require some internal work, more than just readjusting the idle jets. Ive seen people get away with it though, and more often than I would expect. The key is mixing the PCV air below the idle jets like a factory system does. Since there is more air getting in that did not come through the carburetor, the throttle will need to be slightly further closed for the same idle speed, and the idle slightly richer. The transfer ports are not adjustable though. Transfer ports, along with the idle screw ports, are typically fed from fixed orifices. In theory you would have to make changes there. In practice, I have seen cases where those were already a little too rich and it just worked.

 

 

  I have also seen someone plumb the PCV valve into a specific intake runner, instead of a common area which feeds all cylinders, because it was convenient; like a barb fitting that was intended to be a relatively static vacuum source, like power brakes, HVAC or for a vacuum modulator supply. The end result is lean misfire in the specific cylinder which that intake runner feeds.

  Tom Mooney

[NTX5467]

"Lean misfires" are hard to notice, unless you know what you're seeing.  I once had the Camaro hooked to a big Sunn machine and was trying to get to the low percentage of CO that was best for emissions.  I could adjust the idle mixture leaner and leaner, to get to that low percentage of CO, but when I got to a certain point, as the CO digital display still decreased, the HC display went wild.  Jumping from one reading to another with each new number, as fast as it could respond.  THAT was lean misfire, but the engine did not act like a misfire from a fouled spark plug, it just quivered a bit more than normal.  So as i richened things back up, the CO went up and the HC readings went back to normal.  The engine idled a bit smoother, too, as normal.

 

Just my experiences,

NTX5467

[1965rivgs]

56 minutes ago, NTX5467 said:

"Lean misfires" are hard to notice, unless you know what you're seeing.  I once had the Camaro hooked to a big Sunn machine and was trying to get to the low percentage of CO that was best for emissions.  I could adjust the idle mixture leaner and leaner, to get to that low percentage of CO, but when I got to a certain point, as the CO digital display still decreased, the HC display went wild.  Jumping from one reading to another with each new number, as fast as it could respond.  THAT was lean misfire, but the engine did not act like a misfire from a fouled spark plug, it just quivered a bit more than normal.  So as i richened things back up, the CO went up and the HC readings went back to normal.  The engine idled a bit smoother, too, as normal.

 

Just my experiences,

NTX5467

  Dilute the intake charge to a considerable degree in one cylinder and you have a cylinder misfire, period. It`s not anymore complicated than that.

Tom Mooney

[XframeFX]

52 minutes ago, NTX5467 said:

"Lean misfires" are hard to notice, unless you know what you're seeing. 

I'll resort back to sparkplug inspection. But, it would be nice to have realtime inspection such as a WB Air/Fuel Ratio analyzer. Carb Cheater would be the best tool to proceed. Better than purchasing an entry level PicoScope for secondary ignition analysis. Carb Cheater would have realtime parameters on my android!

Late in 2023, I purchased ignition pickups and attenuators for my 80s spectrum analyzer and can see secondary parade of all 8 cylinders are identical but extremely Lean. There appeared to be some random misfire but my setup not as ideal as a PicoScope.

Most of my trouble shooting is while idling. A vacuum leak will affect all circuits. Will scrutinize PCV operation more.

[XframeFX]

9 hours ago, Bloo said:

That AFB pcv port probably goes to the front barrels even if it physically comes out the back. I hope it does.

I have studied the AFB to death. I'm certain the PCV port taps vacuum out of the rear bores. Too busy to accomplish this at the primaries within the carburetor body. Probably the reason Cadillac used that black phenolic adaptor to extract vacuum out the front.

Early 60s technology!

 

[carbking]

Willis - here is your requested carburetor comparison.

 

EDIT: the 3578 should read 425, not 401. Sorry.

 

Jon

Edited January 24 by carbking (see edit history)

[carbking]

The specification that sticks out like a sore thumb in the above chart is that Buick REDUCED the carburetor size from the 364 to the 401. And then reduced the size of the 364 carburetor the following year.

 

The reduction was on the primary side of the carburetor, which would have the effect of increasing the idle signal slightly.

 

The other specification that to me is significant, is that the change differential on the step-up rods from high vacuum to low vacuum continued to decrease (read - the carburetor was leaned at WOT).

 

Jon