PCV Valve - What?

[NTX5467]

Thank you very much for that information, @carbking !  Very informative for comparisons!

 

Might the "Idle Jet" be termed "Low Speed Jet" (hidden in the bottom of the brass idle fuel feed tube)?

 

I've always felt that a metering rod carburetor could be tuned a bit finer with the metering rod diameters rather than a fixed jet.  Interesting that the metering rods became a fine-tuning device when they became basically "straight" rather than stepped.

 

Thanks again, @carbking, much appreciated information.

NTX5467

Edited January 24 by NTX5467 (see edit history)

[60FlatTop]

On 1/23/2024 at 6:51 PM, carbking said:

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).

 

A statement aimed right at my little heart. Back in 1968-69 when I wasn't making steam in the bowels of Uncle Sam's ship I studied the same kind of exciting stuff I curl up with today. At one time I had two courses going one was an International Correspondence Schools (ICS) Automotive Tune Up and fuel Systems, the other Intermediate Algebra and Analytic Geometry from the Navy school in Madison, WI.. I remember how frustrated it was to read about the drill number size one had to use to cure the hesitation in a 1949 Plymouth carburetor. That was the straw that pushed me into dropping the course and turning to magazine articles in Hot Rod. It took a while for me to figure out that it never really was about fixing an old Plymouth. It was about knowing why the procedure would fix the Plymouth and how it applied the other carburetors and maybe even fluid flow in general. Once I figured out concept and detail could run very well together. It even worked with the math course where the answer to the equation was another equation. The carburetor one took a little longer.

 

I have stayed with the idea of fixing the original in most instance although I have mixed a few internal parts, with intention and knowing I could reverse it.

 

 

[Frank DuVal]

On 1/21/2024 at 11:32 PM, Bloo said:

Also, early systems that used an orifice instead of a PCV valve plugged the orifice very quickly.

I will take exception to this. Corvairs used an orifice (.062") from 1964 to 1969. (And turbo models .089" from 1962 to 1966). I have cleaned very few clogged orifices over the years of working on them. And lots of these cars were neglected back in the 70s/80s when they were cheap (free to $50) with lots of blow by and the orifices were not an issue. 

[Bloo]

I'm not doubting you, but I think those (as well as some foreign jobs with not-quite-typical PCV systems) must be outliers. Orifices sure didn't last long on American V8s. The PCV hoses and  carburetor passages themselves can be as big as your little finger and still occasionally plug up.

[NTX5467]

In the 1990s, when we suddenly started to have oil consumption issues on Chevy V-8s, "Engineering" sent us some pcv valves to try on our customer's vehicles.  They were modified pcv valves, cut apart and gutted, with a small hole in the bottom.  Probably about .060" or so?  I think that helped some, but did not fix the issue.

 

I wondered about the fixed orifice rather than a variable orifice, but figured the EFI was compensating for the differences.

 

At that time, I think the ultimate issue was "ring flutter", with the thinner (low drag) rings of the time.  Chevy even bought back some vehicles to use in their testing.  One Corvette I read about could be made to have 1000miles/qt or 3000+miles/qt depending upon how it was driven.  If the driver drove around town with the manual transmission in one gear, using the throttle to vary rpm and road speed, not upshifting, then under low load, high-vacuum conditions, more oil consumption.  Highway cruising, steady rpms and low loads, much less consumption.  Adjustments to ease upward the spring tension slightly, plus a change to the bottom/scraper area of the oil rings, was supposed to have fixed that issue.  Apparently things which were not around in the 1960s when wider rings were used.

 

Enjoy!

NTX5467

[XframeFX]

On 1/19/2024 at 3:38 PM, NTX5467 said:

pcv is a variable vacuum bleed situation.  Little flow at high vacuum, more flow at low vacuum. 

Thanks All for expertise shared here.

I quickly learned the PCV Valve is more than a check valve.

 

- So, including function as a check valve, the PCV Valve is more like a 3-Way Valve.

- Yes, I was aware it had to rattle to be deemed "Good".

- Failure mode is indeed Oil Mist dragged through the plumbing especially if the baffle is in adequate.

- All those PCV Valves that tested the same on the parts counter are probably "Good" including the Echlin valve on my Nailhead now.

- Location of PCV Port is preferred at the Carburetor Primaries.

- Function as a check valve to handle incidences of back-fires.

- Availability of MEWagner adjustible PCV Valve and tech info there.

 

I forgot about power brake booster still not functioning after re-installation. So, will deal with that before condemning the PCV Valve and AFB Carburetor. In fact, I wonder how many 1963 power boosters oit there function without a vacuum leak?

[telriv]

MOST PCV valves normally is  are located at the secondary side of the carb.

In some instances it's at the front as seen on the Edelbrock replacements.

 

Tom T.

[NTX5467]

In one respect, which side it's on might be more of a convenience for the engine plant engine dressers.  Plus related material costs.  As long as the valve sees manifold vacuum, that's all that matters.  Chrysler (which used the AFBs OEM) chose to use an intake manifold runner for their power brake vac source, which is probably why Carters have the front pcv port on them?  That's my theory on the vac source issue.

 

Where the power brake vac tap was and if it was combined with the hvac/cruise control vacuum tap "trees", tended to be a carline engineering decision, I suspect.  Which could vary a bit by the model year and platform.  NOT to forget air cleaner clearance of such trees, too!  Sometimes, "real estate" back there could be tight, vertically and horizontally!!

 

NTX5467