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MG MGA - carburator problem

Installed by rebuilt carburetors today and attempted to tune them. I noticed that fuel was leaking out of the jet adjusting nut on the bottom of the carburetors. Attempted to tighten the adjusting nut and it will spin indefinitely. In fact, the adjusting nut does not move but spins with the jet bearing. What can I do to repair this and is it something that the carberator rebuid caused. Do I bring back the carburetors to the shop or do I buy a new jet bearing kit.

Michael Dvorkin
michael dvorkin

If the carbs were rebuilt by a 'professional', then I would be taking them back. Which carbs are they, SU I presume? If they are the type with the flexible pipe to the jet from the float bowl, they definitely should not leak as they are one piece. If they are the earlier type, the jet adjusting nut may be turning the whole jet adjusting whatsname, which is sealed only by cork washers, and would need further investigation. BUT, if you paid someone to rebuild them, I would be taking them back, and would not interfere with them.
Matthew
Matthew F.

Try tightening the hex fitting just above the mixture adjusting nut. There is a packing washer that needs to be compressed enough to allow paarts inside to come together tightly. If it's not tight the jet could turn as you describe, and it could keak. See here:http://mgaguru.com/mgtech/carbs/cb106.htm
Barney Gaylord

Hi Michael. It sounds like you have standard SU H4 carbs. It appears that whoever rebuilt your carbs overtightened the jet adjusting nut in an extreme upward position. So now the adjusting nut is jammed onto the jet bearing. Consequently, when you turn the adjusting nut, you turn the entire jet bearing. This should not happen! With the current jet position the mixture would be extremely lean, and the engine would likely not run,or would run very poorly. Whoever rebuilt your carbs has apparently done the assembly work incorrectly! Was the rebuilder familiar with SU carbs and how they work?
If the rebuilder doesnt have experience with SU carbs, I would ask for a complete refund, and take your carbs to a mechanic who knows SU carbs. Since you paid good money to have your carbs rebuilt, I would take them back, and let the rebuilder know that the carb rebuild is unsatisfactory! Cheers! Glenn
Glenn

Hi Barney. in your tech notes, you mention replacement jet gland O-RING seals made out of teflon. Where can one purchase these teflon seals? Thanks! GLenn
Glenn

If the large nut (7/16W/1/2BSF/13-16")that Barney mentions is tight, then one or both of the copper washers which seal the jet bearing assembly is missing. One is a flat washer above the top jet bearing, the other is a very narrow one between the lower bearing and the big gland nut.
FRM
FR Millmore

The teflon O-rings came from:
Tom Bryant. P.E.
272 New <eadows Rd.
W. BAtn, ME 04530
(207) 443-6338 (eve)

He advertised in the NAMGAR magazine MGA! "Teflon seals for Type H SU jets, 1/4" ID, $1.50 each". Each "teflon seal" is actually two small teflon O-rings, $0.75 each, eight required to rebuild two carbs, $6.00 total. Cross your fingers and hope he's still suppling these parts.

I bought them in 1998, and again in December 2000 for another carb set, spares, and a few for friends. They never stick or leak, and never fail, so I have not needed any more in the past five years, still have enough for 4 carbs.

I just measured a few, and the are .240" ID, .070" thick, about .375" to 380" OD.
Barney Gaylord

re: Teflon O-rings:
I just measured a few, and the are .239" ID, .070" thick, .379" OD. If anyone needs a large quantity, they are McMaster Carr part number 9559K15 (Same as 9559K1-010), $14.50 for package of 50 pieces. Good for temperature -100 to +500dF.
Barney Gaylord

Thanks for the O- ring info Barney
Glenn

This thread was discussed between 25/12/2005 and 26/12/2005

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