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MG MGB Technical - Vacuum Leaks?

I am still sorting vacuum leaks on our (stock) 1974 B/GT after removing the cylinder head for replacement of valve seats and exhaust valves. I've tried spraying carb cleaner, and used a propane torch around the usual suspects, intake manifold, and carburetors. After testing, I have a new gulp valve ordered.

Also, after rebuilding the carburetors, the front carb seems very cold to the touch with some condensation forming when the engine reaches operating temperatures. I am suspecting an over rich mixture, but have double checked the enrichment valve, and all seems in order.

Suggestions, and methods welcome?

Regards,

Larry C. '69 midget & '74 B/GT
Larry C '69 Midget

Both carbs should feel cold with the engine running. If they feel different to each other then they are flowing differently - either air-flow, mixture or both. How are you checking the mixture?
Paul Hunt

Hi Paul,

My preliminary setup for my HIF's is to turn the jets down two turns from the bridge, and then use the lifting pins to adjust and this usually gets things pretty close. Final adjustments are usually made with "colour tune" to meet the emissions test. However, with the vacuum leak/s it has been difficult to get to that final stage.

I'm off to the garage for additional checking and testing. I'm going to have a look at the piston and piston chamber/s to insure they are moving properly as a probable cause.

Thanks for checking in,

Larry C.
Larry C '69 Midget

Two turns down, then base tuning for highest idle, then fine tuning with the lifting pins should be all that is required. If you find that one carb needs to be turned more one way or the other to get the highest idle, or to get the correct indication on the lifting pin, then there is a problem with one of the carbs. A vacuum leak affecting one carb would need that jet to be turned down, i.e. the mixture screw turned further clockwise, more than the other.
Paul Hunt

Paul,

Thanks again for your help. I think we're on the same page with base carburetor adjustments.

In testing I found the check valve between the air pump, and air injection tubes to be faulty (it checked good on the bench, but fail with the engine running). So I installed (7/16" set-screws) in the air injection ports on the head, and then capped the tube between the gulp valve and intake manifold. Things smoothed out a bit so tomorrow I hope to make final adjustments on the carbs.

Larry C.
Larry C '69 Midget

This thread was discussed between 19/07/2014 and 21/07/2014

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