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MG MGB Technical - HIF4's on a 67 manifold

I have a set of HIF4's on a 67 manifold that has the PCV setup for crankcase breathing.

Should I then just cap off the breathing tubes on the HIF's?

And if so, what about the fuel bowl breather tube?

Steve Rechter

I'd buy the "Y" fitting and use the carb tubes. Using the carbs instead of the Smiths PVC should keep oil consumption down plus you won't have too worry about a split diaphragm. Just plug the manifold tap.
Robert McCoy

Actually I took out the Smith PCV and replaced it with a modern inline PCV valve. I figured that taking vacuum from the intake manifold would be more consistent than from each carb.

What about the other ports on the carbs?
Steve Rechter

I think most folks think the carb vent is more consistent than manifold. It is related intake air flow not vacuum. Your setup will work but some folks haven't had good luck with the inline PCVs. Again, most prefer the Smiths which is what I have for my AUD 135's.

I don't know much about the other HIF ports. I doubt you have a vacuum advance as US cars used manifold vacuum. Hopefully you've got a vacuum capsule consistent with manifold vacuum not port vacuum. If it's a UK carb then you likely have a vacuum advance port on the rear carb underneath.

I think there are vents that go to the charcoal canister on later models. You can just use an atmospheric tube like the HS-4's of your vintage.
Robert McCoy

OK, I will use the breather tubes on the carbs and set them up using a 'y' connector to the oil separator.

There is one other small port beneath the breather port on the carbs. Pictures of other cars show these ports tied together with a metal pipe. Finally exiting through the firewall by a rubber hose on the driver's side(LHD).

Is this a fuel bowl vent? Where does the hose finally terminate?
Steve Rechter

I've never worked on HIF's so am not 100% sure. These are probably bowl vents as you say. They wouldn't go into the firewall. I think they went to some sort of a fuel cutoff valve to close the vents to prevent run-on after the ignition was turned off.

You could pipe this with tubing to the point where your originals exited. I think that's somewhere down by the left motor mount. My overflows have been missing since I bought the car so I'm not positive.
Robert McCoy

This thread was discussed between 10/06/2009 and 13/06/2009

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