Thanks this helps clarify things!

The vac port on the HIF and also on late HS carbs is upstream of the throttle plate. Except at full throttle (when manifold vacuum is low), it has nowhere near the vacuum level as that present in the manifold.

[edit] I do use a PCV valve on road cars when running a Weber or Dellorto. Also when using early SUs with no vac port.
However, rather than use the big old Smiths valve I prefer a Toyota style one. Works best mounted horizontally.
Like this:
//www.eziautoparts.com.au/pcv-valve-pcv-013.html

I thought the large port on the HIF44 has pretty much the same vacuum as manifold vacuum.  Is this incorrect?  Is it somehow metered? 

One point raised by OP not addressed yet by any of our responses:  why doesn't the later SU carb, with the PCV port in its body, NEED a PCV valve?

It does not need one because of where the port is, in relation to the throttle plate.  If you have one of those SU carbs you simply don't need a PCV valve because it works fine without one.  This was a unique benefit to the way an SU works and allowed the elimination of one more assembly which could wear/fail in the field.

Hi John;

I installed the newer Smiths PCV valve years ago as the PO had removed it.  It's a similar setup to Doug's car.

Anyway, here is a link explaining how it works:


//mgaguru.com/mgtech/engine/cv103.htm

Steve, as Malcolm said, that's a Minor engine bay.  It was just the first clear picture I could find on the web showing the Smiths PCV.  Sorry if it not being a Mini caused any confusion.

The picture below is of my car's engine bay about a decade ago.  It also has the Smiths PCV but it is the earlier thick flange type.  It now has the later type shown in the Morris picture above as not all the thick flange parts are still available.

Looks like a Morris Minor engine bay and air cleaner to me Steve.

Hate to ask but is that a Sprite air cleaner? If not do you know what it came from? Steve (CTR)

I am sure a lot of us are using PCV valves.  They were a standard item.  The Smiths PCV valve looks nothing like what you purchase for an American car but the function is the same.  

The Smiths PCV valve can be seen in the picture below.  It is the silver disk looking thing between the oil filler cap and the carb.

This has probably been covered but is anyone out there utilizing a PCV valve on their mini instead of using straight vacuum from the carburetor connected to the breathers on the clutch cover and timing cover?  It seems it would make sense to use a valve to control the amount of vacuum pulled at every given moment.

John