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MG MGA - Float chamber flooding

Gas recently started flooding out of the rear carburetor on my 1961 MGA. In the past have disassembled the float chamber and solved the problem by freeing the lever.

When I disassembled the chamber everything appeared correct, the lever was not sticking and the float was floating. When I manually held the lever up, no gas was pumped when I turned the key on. This did not solve the problem yesterday as the gas continued to flow from the overflow pipe. From researching the archives, I understand that the problem could also be related to a faulty needle. What I don't understand is if the float chamber is working properly, once the chamber fills with gas, the valve at the top of the chamber should be preventing the gas from overflowing. What am I missing?

John Smith
John Smith 3

I forgot to mention that I am using the same SU fuel pump for the last 25 years - so I don't think fuel pressure is the source of the problem. Also, I recently had some problem with coagulated gas in the fuel tank which I took off and had cleaned. At that time, I added a fuel filer on the carb side of the pump.

John Smith 3

Do not confuse the needle with the needle valve

The needle is in the main carb body and meters the fuel whereas the needle valve is in the top of the float chamber and closes off the fuel supply when the level raises the float. It is this "needle valve" that is allowing fuel to pass and it can only exit through the overflow.

With the other items checked it would be wise to buy a new needle valve and istall that
Robert (Bob) Midget Turbo

John - You either have some debris in the needle valve that is preventing the needle from seating properly or you have a needle that is worn to the point that it will no longer shut of the flow of fuel. As for the float lever becoming stuck against the needle, that is caused by excessive float lever drop. See the article, Float Lever Drop Adjustment in the Other Tech Articles section of my web site at: Cheers - Dave
David DuBois

I've had that happen before and it turned out to be a tiny bit of grit in the needle valve, preventing it from seating properly as David suggested. I solved the problem by removing the needle valve, gently cleaning it off, and then reinstalling it.
Andy Bounsall

Okay, thanks to everyone for your comments. I will try cleaning the valve this weekend and let you know how I make out.

John Smith 3

I had the same problem and discovered that the float, while floating in the chamber, actually had filled partially up with fuel. I strongly recommend that you removed the float and shake it to make sure it is empty. If holding the fork up stopped the fuel flow, it sounds like the float to me.
DB Brough

Put the float in hot water, the heat will cause air/petrol vapour to expand and watch out for bubbles if you have a leak.
J H Cole

I had encountered the same problem even with new needle valves fitted. I solved the problem by replacing the standard needle valves with the magic grose jets.( I doubt very much whether the judges will look inside the chambers for originality).

F Camilleri

I've been running the same set of Gross Jets for 20 years and 210,000 miles, and never a problem. I do have a very clean fuel system, and a tiny filter before the aftermarket fuel pump. I hear tell the Gross Jets can sometimes stick either open or closed with the tiniest but of rust flake, so if you have any debris in the fuel tank you should use a good filter before the Gross Jets.
Barney Gaylord

Gross Jets definitely eliminate the problem associated with excessive float lever drop (there is no long needle to jam against the lever). I have read of problems associated with Gross Jets in recent years after they were taken over by a new company. I have not had any experience with the new ones (haven't purchased any recently), so I am just tossing this out as a heads up. Cheers - Dave
David DuBois

I run the standard SU valves. Never had a problem. My money goes on a semi-submerged float as previously said. Also, could a badly adjusted (bent) valve lever be the problem?

A punctured float can be mended very easily. No need to buy new. Many pre-war MGs have floats that are more solder than copper!

I have been advised to avoid Gross jets as they stick. Seems to tie in with some of the comments now being posted.

Steve Gyles

Steve, my RAF friend, I beg to differ. The way grose jets are made makes it almost impossible for them to stick either open or closed. Like anything else, their only enemy is dirty fuel with tiny particles jamming the ball bearing.

F Camilleri

No problem Frank. I have never tried them so cannot speak with any authority whatsoever. There was a thread several weeks back on Grose jets. At that time I was ordering new rubber bushes between the float chamber and main body. I asked my supplier about adding a set of the jets to the order and he advised me against them, saying he was having problems with current batches and, if my SU valves were okay, to leave them in place.

Steve Gyles

Well Steve, of course you did the right thing. You know the saying, 'If it ain't broken don't fix it. Nice talking to you Steve.

F Camilleri

Okay -- I couldn't wait for the weekend so I pulled the float and as suggested, it was partially full of fuel. Turned out to be a much simpler fix than what I was expecting. As long as my solder job holds up I will be back on the road by Saturday. Unfortunately the car is just off warranty so I had to do the work myself.
JRS Smith

"Unfortunately the car is just off warranty"...
are you being humorus or did you, in fact, have some type of warranty?

Just curious,
G T Foster

Dear GTF:

No just a lame attempt at humour. I guess if you have owned a car for 42 years the warranty has probably expired. Also, those British Leyland dealers are really hard to find.

Once again, thanks to everyone who responded to my problem. Not only did you identify the problem but you told me how to fix it. You guys are great.

John Smith 3

This thread was discussed between 12/10/2010 and 15/10/2010

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