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MG MGB Technical - Anti Run-on Valve

I just bought a 1974 MGB. the Anti run-on valve is pumping fuel out the drain hose when the key is in the on position. this is without the engine running. any help would be appreciated
dww Ward

You have a needle valve that is not closing or a sunken float in the carburetor float chamber. Cheers - Dave
David DuBois

As David says it is a carb float or float valve problem, pushing fuel through the anti-runon valve via the charcoal canister, nothing to do with the valve itself. If twin carbs (American changed to single during 74) remove the overflow pipes that go to a Y connector and then the canister to see which one is leaking. They should be HIFs, which means you have to take the carbs off and remove the bottom cover of the faulty one, which will need a new O-ring. I think the single carb is also attacked from below but uses a gasket instead of an O-ring, which may be capable of being reused.
Paul Hunt 2010

Agree with all - I had the same problem on my '73, and it turned out to be both floats.
Patrick Callan

DWW-
Carefully inspect the shut-off needles and their seats in their valve bodies for any signs of damage. Because both the tip of the shut-off needle and its seat in the valve body can be easily jammed or damaged by debris, an event that is the most common cause of carburetor flooding, you should consider replacing the shut-off needles with a Viton-tipped version (Burlen Fuel Systems Part # WZX 1097). Because they will withstand a fuel system pressure of about 10 psi, these are a distinct improvement over their predecessors which could withstand a fuel system pressure of a mere 6 psi.
Stephen Strange

This thread was discussed between 23/06/2010 and 05/07/2010

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