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MG MGB Technical - Small pipe on carb manifold

I have a 1974.5 MGB with the DGV Weber carb conversion and Longflo foam air cleaner set up. I noticed that on the right branch carb manifold there is an inch high thin tube with nothing attached (it looks like a hose should be attached there) . The tube does draw air as I can feel the vacuum when I hold my finger over it with the engine running. As of now I have it blocked. I know it's not for the vacuum advance. Any idea what it's for, and should I just leave it blocked? Funny thing is the engine seems to run a little better when it is not blocked, pulling more air in I guess. Any ideas? The air filter is new.
Tom

Tom. That, most commonly, is the take off for the brake servo unit (power brake booster) on the rubber bumper cars. If your car runs better with it open, look to your mixture--it is too rich. I had a vacuum leak on the rear leg of the intake it it caused number three cylinder not to fire. If yours is actually running better, check the plugs and see if one and two are getting carboned up. Les
Les Bengtson

Les,
I've been having a problem with #3 fouling, black soot. I have tried to adjust the carbs mixture. I guess I didn't get it right yet. Thanks for the help.
Tom

The servo pipe is what I would call fairly stout, at the rear end of the manifold and usually angled backwards. It could be the take-off for the distributor vacuum pipe, running-on control pipe that went to the anti-runon valve, or yet again for the gulp valve, all small bores. And FWIW early cars used one for the overdrive vacuum switch. Whatever, if it isn't connected it should be sealed, it *will* lead to rich running even if the mixture is correct at idle.
Paul Hunt

This thread was discussed between 21/10/2004 and 22/10/2004

MG MGB Technical index

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