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MG MGB Technical - Twin SU carbs leak fuel

This is the third time I'm starting a new thread about the same problem. Seems I can't find the previous 2 threads.

Anyways, I have a 74 1/2 CB B and I can't get the car to idle. I initially noticed that fuel was leaking out of the canister.

I have disconnected the fuel pump and the car doesn't even start. After reconnecting the fuel pump, I disconnected the carb overflow line and turned the car on and the fule pump eventually filled the carb and the fuel came staright out the overflow line.

I also tried rapping on the bottom of the carb.

So, I guess my next step is actual dismantling of the HIF 4s.

Thanks all for your past and future advice.
ChuckE

Ok, you now know it isn't coming from the tank to the canister via the evaporation system. Now you have only two sources for the problem- the fuel pump could be overpressuring ,or one or both float chambers/valves are the problem.If you have access to another fuel pump, it may save you tearing down the carbs. I did the carb route and the problem persisted. I even switched from HS4 to HIF and the problem persisted. I switched back and I bought a new pump and solved the problem.I hope it is the carbs, as they are cheaper to service. You are on the way to a solution. Keep us posted.
Ken R
Ken Rich

Someone adviced me that an aftermarket pump will usually put out a much higher PSI then the 3~5 PSI needed for the MG. But seeing the fuel leak out of the carbs, it just seems to dribble out.
ChuckE

Ken,

Wouldn't the fact that the car doesn't even start without the fuel pump connected point to the carb? Unless there was no fuel in the carb when I disconnected the fuel pump.

Hmmm.
ChuckE

Even w/o the fuel pump, if there is fuel in the float bowls at a high enough level, the car should start and run for a minute or two, then it will literally run out of gas. It sounds to me like you have a sticky float. The overflow for the float bowls goes to the cannister, so fuel coming from the cannister indicates a likely stuck open float. Do you have an aftermarket pump, or the real deal? The aftermarket pumps can overpower the float needles, but a pressure regulator takes care of that problem.

Haynes makes a carb manual available through Moss and others, which also covers various Webers and Zenith-Strombergs. It also has the SU needle chart as an appendix in the back. Highly recommended.
Paul Konkle

I don't know if the Fuel pump is OEM or not. The PO did say he replaced it.
ChuckE

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ChuckE

This thread was discussed between 08/05/2002 and 10/05/2002

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