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MG MGB Technical - HIF Carbs, Crankcase breathers

I was hoping that I could get your opinions on this. My 77 B was converted to HIF carbs. I have since added conicle K&N air filters and AAA needles to counteract rich running at idle and lead at higher RPMs. The PO had removed most of the smog stuff. The crankcase breather is terminated into the (removed) air pump's filter and the HIF ports where the breather should be connected are blocked off. My question: Will I gain anything by connecting the HIFs to the crankcase breather tube as they should be? Thanks for your help. Ernie
Ernie C.

Yes. Actual crankcase ventilation. I think the way you describe it there isnt much now. In the original system make-up ventilation is drawn through the tube on the back of the rocker cover from the evaporative cannister. On the older pre-18V engines it is through a vented oil filler cap. Both are engineered to have just the right size opening. The tube from the front side cover on the engine should connected to the the two carbs. This provides the vacuum to draw the vapors from the crankcase, and replacement air via the push rod openings in the head and thence from the valve cover. The Moss Catalog has a good diagram of this.The air pump filter should be removed for "storage", in case you ever want to re-smog it. Regards, Andy
Andrew Blackley

Andy

Thanks for your feed back. I had assumed that the crankcase breather was the output of the system, so I thought the air filter was a good place to end the breather. In the past I have seen on older MGs the breather connected to a pipe that was open ended at the bottom of the engine. I just assumed it was a drain. After reading your post, I did some research and found that at road speed, a vacuum is produced at the end of that breather pipe to provide the vacuum necessary to put the "positive" in PVC.
I'll connect my system up this weekend. Thanks for your help. It's great to learn a little more each day!

Ernie
Ernie C.

Could Andrew Blackley be a little more specific as to where in the Moss Catalog he is referring.
Jack

Jack: Yes indeed. I have an old catalog here at work, MGB-11. On page 14, which is headed "Emission Controls" at the top (and is the same in the newer catalogs as well) there is the diagram to which I was refering: that for the 1970 to 1974, the hoses in question are numbered 50, 51, and 52, not forgetting #49, the "Y" fitting. Hose #70 runs from the valve cover to the evaporative cannister. If the car is so de-smogged that this is missing too, then one could either fit an air filter to the end of the hose (actually a large fuel filter should work) or use an older style oil filler cap and plug the line from the valve cover.

Regards, Andy
Andrew Blackley

Andrew,

Many thanks, that will save me a frustrating search.
Jack

I've now had a look at the Moss catalog and can see the details Andrew highlighted. Many thanks Andrew.

Surely the simplest way to deal with this little matter is to fit that earlier breathing oil filler cap.

Compared with that, everything else seems a bit messy, or have I missed something.
Jack

This thread was discussed between 08/05/2002 and 09/05/2002

MG MGB Technical index

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