MGB & GT Forum

Yes, you have a float valve "stuck open", but, the effects that you observed may be the "tip of the iceburg".

Gasoline can be pumped into the charcoal canister as well as diluting the engine oil, in the crankcase.

If it were mine, I would verify the carburetor float(s) have no damage and/or liquid inside the floats, if they are the brass floats air inside, vs solid plastic floats sometimes used in carburetors.

If you don't know when the the needle valves which are mechanically closed by the carburetor float(s), have not been changed within 10,000 miles, and/or the fuel supply system is pumping dirty fuel into the carburetor(s), I would replace them.

I keep this summary available, after my 1977 MGB contaminated the fuel system with water condensing in the fuel tanks and the steel fuel lines rusting so bad, that there was very little space for the fuel to flow through the fuel lines. Yes, this can only get this bad when your local fuel has alcohol as well a gasoline in the fuel:

Copper Nickel Fuel Line

If you have the original steel MGB fuel supply line from the tank to the carburetor, and your area has alcohol in the motor fuel, you are set up for a problem:

Before alcohol was mixed in the gasoline, the gasoline "floated" on top of the water, and most of the time, there were no problems.

Alcohol and water "mix" together, into a solution, and then the "alcohol-water solution" mixes with the gasoline, which rusts steel parts.

MGB "original equipment fuel lines" are made from steel. When I looked at my fuel lines, they were almost completely filled with rust.

You will find that your local auto supply will have 5/16 inch outside diameter, copper-nickel alloy fuel lines, which will solve this problem.

You will need to have your fuel tank cleaned at the radiator shop, and probably have the steel fuel line that goes down the bottom of the tank removed and replaced with the copper-nickel alloy tubing.

Then replace the fuel supply line, all the way to the carburetor(s) with the copper-nickel tubing. One roll of 5/16" OD copper-nickel fuel line which costs about $15 here in CA, has enough fuel to replace both the fuel supply line and the fuel tank vent line to the charcoal canister. There was even enough for a third, return line, for my next project, a GM 3.4L V6 (160 hp) engine, with electronic fuel injection, which requires a return fuel line all the way back into the fuel tank.

If your car has the charcoal canister and fuel tank vent line from the tank to the engine compartment, that line will need to be replaced as well.

Roger N. Tanner, Professional Engineer (retired)
Ventura, CA

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Roger N. Tanner
Professional Engineer, Retired