[chrisp]

Opinions on ditching the F fitting vacuum source & using what i have is a non original center carb rear vacuum source for PCV valve signal.

[Kenth]

Could work if you have a 1/4" NPS hole for a 90° 1/4" NPT fitting for a 3/8" hose.
Would look odd though.

[Goatracer1]

Why change something that works? Plug the carb vacuum source.

[GtoFM]

How I understand it is the F fitting references vacuum from each plane of the manifold to give an average. If the same result could be achieved from the carb base, why didn't Pontiac engineers do it that way? What am I missing?

[Kenth]

Originally Posted by GtoFM

How I understand it is the F fitting references vacuum from each plane of the manifold to give an average. If the same result could be achieved from the carb base, why didn't Pontiac engineers do it that way?

Lack of space for a 1/4" 90° fitting between center and rear carb?

[chrisp]

Thinking it would be better distribution of the crankcase heat & fumes rather then into the unbalanced intake runners.

[chrisp]

Originally Posted by GtoFM

How I understand it is the F fitting references vacuum from each plane of the manifold to give an average. If the same result could be achieved from the carb base, why didn't Pontiac engineers do it that way? What am I missing?

The factory center carbs do not have the port , as stated this is a non original center carb on a 461.

[Kenth]

Originally Posted by chrisp

Thinking it would be better distribution of the crankcase heat & fumes rather then into the unbalanced intake runners.

Look closer to the upper and lower plenums under the carbs and you´ll notice that there are no unbalanced distribution of crankcase fumes to singel intake runners with the original setup.

And, most original center Tri-Power carbs has a 1/8" NPS threaded port back of the throttle plate for a fitting to distributor ignition vacuum advance.

[pfilean]

Early PCV option was a plate (probably a phenolic something or other) about 5/16-3/8 thick under the center carb. Then plates (thick gaskets) under the end cards so the larger air cleaner would still fit level on the three carbs. The PCV was then a tube from the front center of the center carb plate and the plate was open to both bores. PCV was the tube curved to the passenger side then a hose back to the PCV valve in the old draft tube hole. Tube was flattened to fit into the plate and sealed to not leak. It was a kind of delicate piece and probably a service problem as mechanics tried to pull the hose off the tube. Then in 63 or 64 the design changed to the F fitting. Haven't seen one of those old things on eBay for years. Last one may have been the one I bought so I could keep an original look.

[Kenth]

Like this:

[GtoFM]

OK with all the above understood, and the front carb throttle body ftg. was used for the brake booster vacuum, then why didn't the rear carb have the same throttle body as the front carb to be used for the pcv?

[Kenth]

Location of the ignition distributor?

[pfilean]

That's the picture Kenth. I was on the wrong computer to find the picture.

[Dick Boneske]

Every center carb I"ve seen has either a 1/8 or 1/4 NPT hole in the base. Simply find a hose barb fitting to match the center carb base hole and run a 3/8" ID hose to the PCV valve. There is plenty of clearance between the rear of the center carb and the rear carb.

[carbking]

Use the rear fitting for the PCV. If you also need distributor vacuum, use a hollow stud.

Jon

[Kenth]

Some years rear Tri-Power carb lacks hole for a fitting.