Later MGBs didn't use the PCV valve, just continual suction from ports on
each SU, through a Y-piece, to a vent on the front tappet cover. UK models
then had a breathing oil filler cap which completed the system. US models
had a restricted vent on the rocker cover which was piped to the charcoal
cylinder, and from there to the tank, anti-runon valve and carb float
chambers. The valve in its normal running position allowed a flow of fresh
air through the system, and in its 'just switched off' position blocked that
port which meant the suction from the carbs was applied all the way back to
the float chambers to suck the fuel out of the jets and stop the engine,
preventing runon.
With the UK system, at least, removing the oil filler cap causes the revs
(on a correctly tuned engine) to drop slightly, and you can feel the partial
vacuum by putting the palm of a hand over the open filler. If yours doesn't
do this then either the vacuum is not 'getting through' or is being filled
by a leak elsewhere.
----- Original Message -----
From: "Andrew B. Lundgren" <lundgren@byu.net>
To: "Ruggiero Larry Lt Col AFRC/XPXS" <Larry.Ruggiero@AFRC.AF.MIL>
Cc: <mgs@autox.team.net>
Sent: Friday, November 15, 2002 3:16 AM
Subject: Re: Valve Cover Venting
> Thanks for all the great info. I have a the vent from the tappet chest
> cover piped up to the intake on my weber with no pvc valve. I have
> been trying to figure out why I get oil all over the top of my aluminum
> valve cover.
>
> I had to switch from the chrome oil cap to the old black vented one
> because of the oil mist all over the chrome cap made it so slippery it
> was almost impossible to remove the cap.
>
> I will buy a PVC valve and hope to see the problem go away!
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