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MG MGB Technical - Where does the fuel go?

After a good usage and shutting down the engine why does my fuel pump go crazy ticking to refill the carbs just a couple hours later? Does the fuel drain back into the tank or flow into the cylinders?
Bob Ekstrand

Sure it's not just repressurizing the line?

There would be some float chamber evaporation, but there's no way I see that you could siphon the fuel out of the floatbowls. Equally, there should be now way that it should flow into the intake, save for thermal expansion, and I don't believe there is enough expansion to put liquid into the intake.
greg fast

It must be evapouration , they are over the manifold and there will be heat soak. I imagine it condenses in the overflows and the runs out.It does give you a clue that the fuel pump is working.
S Best

Bob,
There are two factors involved: evaporation and thermal expansion. Gasoline has a very high evaporation rate, especially at engine temperatures. So much of the fuel in the float bowls go out the vent tubes as vapor. Also gasoline loses roughly 1% of it's volume with every 10 deg F reduction in temperature. Assuming the fuel in the bowls is at 150 deg F when you shut down the engine and it cools to 70 deg before the next start you've lost around 8% volume.
Bill
Bill Boorse

I've heard the fuel *boiling* in the float chambers on my V8 after a hot run, vapour pouring out of the overflow pipe, and lots of chattering on a restart. But after a cooler run the restart is usually just a couple of clicks. The roadster usually only gives lots of chattering after not being used for about a month and is much less affected by heat. I can imagine that expansion from heat soak *could* overflow into the cylinders, but that would make for difficult hot starting, which I have never noticed on either car.
Paul Hunt

Isn't there something about the quality of the one way valves in the fuel pump? Backflow into the pump perhaps, draining the lines?
Paul Hanley

This thread was discussed between 28/04/2005 and 29/04/2005

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