'63 300HP CV-590 PCV valve function questions

[Paul B.]

Hi,
My stock '63 300 4 speed has a CV-590 PCV valve on a T fitting, see pic, the second hose goes to the brake booster, forgive the non judging clamps.

The valve is angled down a few deg at the threaded end to allow the the brake booster hose plenty of clearance under the throttle linkage.

When I get the motor good and warm, especially if I've been running it up through the gears then on the highway, the idle will hang at 1000, or sometimes 1200 RPM when I come to a stop, but if I tap lightly on the PCV valve, it drops back down.

It rattles freely when I shake it, I tried cleaning it with some spray carb cleaner, then some compressed air, but still the same. I can try soaking it, but I've been reading that there were reproduction CV-590 valves that were not very good, is that my issue, or possibly the downward angle of the valve?

Many thanks,
Paul

CV-590 2.jpg

[Arland D.]

Re: '63 300HP CV-590 PCV valve function questions

Paul,

My 340hp pcv is installed at the AIM specified 45 degree angle. This picture shows a 300hp pcv with power brakes that uses a different style brass fitting setup allowing more angle adjustment than the one you show on yours. You are right that the almost flat angle of the pcv could be problematic.

[Paul B.]

Re: '63 300HP CV-590 PCV valve function questions

Hi Arland,
Thanks for the reply. I looked at the diagram in the AIM (C141), I see the 45 deg mounting angle reference, opposite inclination to mine, but is the angle important to the correct functioning of the valve, or is it shown more for hose routing purposes?

All the best,
Paul

PS. The T fitting in the picture of the 300 that you posted appears to be the same as mine, but with the addition of a 90deg fitting to change the orientation.

[Gary B.]

IMG_0301.jpeg

[Duke W.]

Re: '63 300HP CV-590 PCV valve function questions

The '63 PCV system is configured completely differently from the '64/'65 systems (which did not have PCV valves) and the, again, different '66 system.

If the valve rattles when shaken it should be okay, and it's also okay to soak an all-steel OE valve in carburetor cleaner. Reproductions? I have no experience.

A common cause of AFB changing idle speeds every time the throttle is returned to the idle position is wear of the primary throttle shaft bores. This can cause the shaft to shift slightly altering the flow area, which is why the idle speed changes. A quick "kick" of the throttle pedal will usually return the normal idle speed. A stiffer return spring is a temporary crutch, but the untimate fix is to bore the throttle shaft bores oversize and install bushings.

As far as the brake booster vacuum hose routing is concerned, the AIM shows a bracket attached to a valve cover holdown cap screw that locates the hose and routes it, probably above the throttle shaft, but it's not clear from the illustration (Sect. J-50 Sheet 3.00).

It's not clear in your photo if your car has this bracket, but my guess is that it is missing. The hose has a specific part number, but I don't know if it's just a piece of generic hose cut to a specific length or a custom molded hose with all the requisite bends.

Since these hoses always see vacuum (other that a possible pressure wave from a carburetor backfire) the engineers deemed that no clamps were necessary.

Duke

[Leif A.]

Re: '63 300HP CV-590 PCV valve function questions

The '63 PCV system is configured completely differently from the '64/'65 systems (which did not have PCV valves) and the, again, different '66 system.

If the valve rattles when shaken it should be okay, and it's also okay to soak an all-steel OE valve in carburetor cleaner. Reproductions? I have no experience.

A common cause of AFB changing idle speeds every time the throttle is returned to the idle position is wear of the primary throttle shaft bores. This can cause the shaft to shift slightly altering the flow area, which is why the idle speed changes. A quick "kick" of the throttle pedal will usually return the normal idle speed. A stiffer return spring is a temporary crutch, but the untimate fix is to bore the throttle shaft bores oversize and install bushings.

As far as the brake booster vacuum hose routing is concerned, the AIM shows a bracket attached to a valve cover holdown cap screw that locates the hose and routes it, probably above the throttle shaft, but it's not clear from the illustration (Sect. J-50 Sheet 3.00).

It's not clear in your photo if your car has this bracket, but my guess is that it is missing. The hose has a specific part number, but I don't know if it's just a piece of generic hose cut to a specific length or a custom molded hose with all the requisite bends.

Since these hoses always see vacuum (other that a possible pressure wave from a carburetor backfire) the engineers deemed that no clamps were necessary.

Duke

Duke,
I borrowed this picture. Routing of the vacuum hose, with the required clamp, is UNDER the throttle linkage on '63s. Later C2s, the hose was routed OVER the throttle linkage when the vacuum port was moved from the driver's side of the booster to the passenger side of the booster. And, there were clamps on both ends of the vacuum hose...'63 - '67.

[Bruce G.]

Re: '63 300HP CV-590 PCV valve function questions

IMG_1326.jpgIMG_1471.jpgThis is routing on my '63 300hp - A/T that was 2022 TF with no deductions on orientation. Bruce

[Paul B.]

Re: '63 300HP CV-590 PCV valve function questions

Thanks for the feedback and pics guys, appreciated!

The carb is freshly professionally rebuilt and otherwise seemed to run fine on my first test drive, thankfully no more seizing at WOT! My spare AFB (non numbers) had the same idle hang issue when good and warmed up, I finally isolated it to the PCV valve, a light tap or two and the revs drop right back down, won't tell you how long it took me to nail that one down...

The weather Gods may not let me drive it again this season, but I'll soak the valve, then reinstall with no angle in case I get a last chance to get out one more time before the salt man starts spreading his crystalized carnage.

I'll also buy the later CV-590C to give that a try in the spring, a bunch of them for sale on E-Bay.

All the best,
Paul

[Timothy B.]

Re: '63 300HP CV-590 PCV valve function questions

Paul,

I think the original valves can be taken apart and cleaned, this would eliminate any issues with the PCV system.

[Paul B.]

Re: '63 300HP CV-590 PCV valve function questions

Hi Timothy,
I'm quite sure that the one that I have is machined from a single piece of steel, but I can certainly take it off and soak it in carb cleaner for a day or so.

If anyone knows how to differentiate an original from a reproduction, I'd appreciate it, my photo is pretty clear, but I can also remove it and take better pics.

Thanks,
Paul

[Duke W.]

Re: '63 300HP CV-590 PCV valve function questions

Duke,
I borrowed this picture. Routing of the vacuum hose, with the required clamp, is UNDER the throttle linkage on '63s. Later C2s, the hose was routed OVER the throttle linkage when the vacuum port was moved from the driver's side of the booster to the passenger side of the booster. And, there were clamps on both ends of the vacuum hose...'63 - '67.

Yeah I missed that. The '63 AIM shows spring clamps, 3829-58. (I can't decipher the fifth digit.) The ...58 clamp superseded 272846 with the AIM drawing change dated 11-8-62, so maybe not even very early cars had this old clamp, and a six digit part number means that clamp was ancient then.

MY 340 HP SWC does not have power brakes, and it never had any kind of clamps on the hose between the rear crankcase vent pipe and PCV valve and none are shown on the AIM sheet for that hose (Section 6 Sheet B 1.00).

Clamps were likely deemed necessary on the PB booster vacuum hose because of the relative motion allowed between the engine and booster due to the flexible engine mounts.

Duke