Stromberg U3 carburetor fuel leaking

[147 Franklin Airman]

My U3 carb is throwing fuel out of the butterfly shaft and i wondered if anyone had any idea as to why this would be? There is also fuel dripping out of the vent hole at the bottom which is be be expected. The float level is about 15/16" below the gasket without the float in.

The car seem to run ok otherwise.

Any suggestions would be most welcome

[odyssey]

Does it come out past the butterfly shaft and bottom vent hole only after you crank the engine to start it and it doesn't start? Or after shutting the engine off when it is not warmed up?

Tom

[147 Franklin Airman]

Hi Tom

Many thanks for your response.

The fuel only starts to leak when I start to crank and leaks both before she starts and during running. It continues to leak after switching off but could just be wet, both cold and when hot.

At times she will start quickly but will often take 20 or more cranks.

Martin

[carbking]

Some seepage out the throttle body past the end of the throttle shaft is quite normal on an updraft carburetor once the engine has been turned off. The fuel in suspension in the intake manifold drops down on the closed throttle butterfly, and seeps out by the shaft.

Leaking past the shaft during a running engine is NOT normal. Since there should be vacuum at this point when the engine is running normally, the vacuum would keep the fuel from leaking past the throttle shaft. I would do a compression test to see if a defective intake valve were allowing exhaust pressure back into the intake. This is a potentially dangerous condition.

Jon.

[147 Franklin Airman]

Thanks Jon

The compression test revealed 65psi in cylinder 4 and the rest were 50 so I may have more than i leaking valve. I will put some oil on top of the pistons to help reveal a bad valve and do another compression test.

She did back fire on me a couple of times the last time I drove her.

Thanks for your help

[147 Franklin Airman]

Hi Jon

The leak has stopped after dropping the float level again and also unsticking the economiser. The valves all check out ok.

I still feel that too much fuel is being passed into the cylinders and the plugs are very black and the exhaust emits water and soot excessively and when she is hot the engine starts hesitating. All inlet gaskets have been replaced and sealed.

I have emailed your company 3 times now and only got one response requesting my address for shipping costs.

Do you have a service kit for the U3, if so how much would it be to ship to the UK?

The Franklin club have very little details on their website about the U3 carb.

Many thanks in advance

Martin