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MG MGA - Carburetor overflowing!!!

I blew a cylinder head this spring and have finally replaced it. Once I got everything re-attached... intake manifold, exhaust manifold, carburetors, etc. After making several checks I attempted to start the engine. When I turned the ignition key, gas immediately began running out of the overflow pipe on the front float chamber.

Why would this happen?
gerard hutchinson

It may be stuck open flow valve in the float chamber lid. Just give it a tap and it may free up otherwise take the lid off and check that the valve lifts freely to cut off the fuel and drops freely to allow fuel into the bowl. You could also have a sunk float as they can and do develop pin holes the float then fills with petrol sinks and wont shut off the fuel. If you do have a sunk float you can find the hole by immersing in boiling water to see a stream of bubbles as the fuel evaporates, you can then solder it and repeat the test.
Hope this helps

AR Terry

I did remove the top and the float is "floating" and moving freely. I did not check the other chamber for comparison.

Also, what valve could be stuck open? and why does the other chamber not overflow?
gerard hutchinson

Pull the float out and shake it to see if there's fuel in the float. I had brass floats in my carbs and one was allowing fuel into the float. It would still "float" but at a lower level and that carb was dumping a lot of fuel out of the overflow tube.
S Jackson

Gerard, on the underside of the lid of the float chamber you will see a forked lever that in operation sits on top of the brass float. This lever controls the flow of fuel into the chamber by lifting to cut of fuel or dropping to release fuel depending on the level of the float (same as the ballcock in your toilet). The valve is of hexagon brass screwed into the lid within which sits a needle valve which should rise and fall freely.
AR Terry

AR Terry,

I did not look at that!! Thank you!!
gerard hutchinson

Your welcome Gerard. Hope you fix it ok now.
AR Terry

Is there anything I can do to "fix" the hex-screw and keep it from sticking?

The photo shows the hex-screws after I unstuck it.

gerard hutchinson

Now that you have it free it will probably stay free until the car sits up again...more than likely it was gummed up due to old fuel.

Or you can replace the needle and seat - they're cheap.
Moss Motors part number - 371-060 . $13.29
Gene Gillam

I changed to Gross valves years ago, after two floodings. Never happened since I changed.


Colin Manley

I changed to Gross Jets 26 years ago, now 375,000 miles maintenance free on the same parts. You do have to keep the fuel clean.

Original Gross jets are still good stuff. The recent replacement parts "Gross Type Jets" are often pretty bad, treat like poison, stay away. I'm not certain that they are all bad, but the odds are not in your favor.

Gerard - The picture that you attached shows there is excessive float drop in the float bowl. The fix for that can be seen in the article, Float Lever Drop Adjustment in the Float Lever Drop Adjustment article on my web site at: The excess float drop can allow the float lever dropping so far that can jam the float in the carburetor, not allowing the float to shut off the fuel going into the float bowl. Cheers - Dave
DW DuBois

Great article. Wish I had read it a few years back when I had the same problems with my frogeye. Would have saved a lot of time.
Graham V

Yes, good bit of knowledge Dave. Now registered in my brain.

Steve Gyles

I'm having a similar problem. Fixed a leaking fuel line at the banjo bolt at front carb. Took car for a shake down. Ran fine then suddenly started dying at low revs. I managed to get home and there was gas pouring out the front overflow tube.
M. K. Davis

Is Dave Dubois' article not of any help?
Graham V

DW DuBois!

The fix you presented has worked perfectly!

Thank you!
gerard hutchinson

This thread was discussed between 04/06/2018 and 02/07/2018

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