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MG MGB Technical - Fuel Leak

Hi I Have a 68 Roadster and have noticed that the overflow pipe on the float chamber is dripping fuel almost constantly. Can anyone please give me some ideas on how to sort this out as apart from using more fuel I don't want me car to go up in flames.

Thanks John
John

John. Have you checked the float bowls to make sure there is no crud in the bowl preventing the float from rising to shut the needle valve off completely? In the past, crud hindering the movement of the float, a bad float, or a bad needle valve have been the most common problems causing fuel to vent out of the overflow/vent lines.

Les
Les Bengtson

Thanks Les I will give it a try
John
john

Change the needle valves.
Iain MacKintosh

i agree with ian but put the grose valve upgrades in they dont leak once set
10 years and no probs
ste brown

Same problem as John, same fix as Ste, same outcome as Ste. -- Fred
Fred Doyen

Don't forget to check your fuel pressure, over if over 4 psi cna push fuel past the float needles.
John H

fred
have you used the metal topped adjustable floats with your grose valves
my dads roadster has them 10 years no probs
my old gt 5 yrs no probs
my new roadsters floats were broken so got later none adjustable ones but the groses wont work due to the slant on the top of it if i set the grose correctly its too high and flows over the needle valve so washered up to lower the float and it wont start so having to get some old adjustable floats from autojumble to cure as i dont wont the needle jets in
ste brown

John - All of the above plus check that the float itself is not flooded. Good luck - Dave
David DuBois

I've seen more bad comments about Grose valves than good, the standard valves work perfectly well, although I'm sure people have found that a new Grose valve is better than a knackered standard valve!

I would disconnect the fuel pump (i.e. where the white in the rear harness joins the whites in the main harness) and run the engine to empty the float chambers and stop, then reconnect the fuel pump. The resultant rush of fuel through the now wide-open valves will often clear any debris that the normal barely-open position of the valves won't. If the pump still clicks occasionally, and after a few seconds (or sooner) fuel starts leaking again, then you do need to look further. With fully non-leaking float valvs the pump shouldn't click more than once every 30 secs. If that cures the problem, but it returns agin in a few days or weeks, then dirty fuel/rusted tank is indicated, if so you should see crud in the bottom of the float chambers. A fuel filter may help, but if it is bad it may block up fairly quickly.

If the overflowing starts again very soon after flushing as described above remove the float chamber tops any way and carefully look at the floats (if plastic) or shake them and listen for fuel sloshing around. If the floats are good then replace the float valves as a matter of course.

If you have a non-standard fuel pump then these can overwhelm the float valves, the original pump only delivers about 2-3psi.

Finally I have heard of engine vibrations causing a float valve to leak, but only rarely, the float chambers should have a rubber coupling to the carb body prevent this.
Paul Hunt 2

This thread was discussed between 04/02/2006 and 08/02/2006

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