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MG MGB Technical - Another fuel overflow problem

I have a 1979 MGB, I have changed out the stromberg for a twin SU HS4 last year. This year when I took it out of storage I noticed that after the engine was up to temp. the front float bowl would spill fuel onto the fender when you reved the engine at a high rpm and let off back to idle. The following are the parts that I have change out so far, two new floats (plastic type), two needle valves and seats for the floats, fuel filter, and one new electronic SU fuel pump( the old pump was a no name electronic pump).
With these new parts I still have the same probem, when I have engine at running temp. and rev it at a high rpm the fuel spills out of the overflow when the the engine reves start to come down to idle. I have checked the archive found some ideas, but nothing that works. Any help would greatful.

Thanks, Andrew


A.A. McFadden

I am definately no expert but my suggestions would be ..

- At high RPM you're float bowl starts shacking and therefore doesn't block the fuel properly anymore
- The fuel pressure gets too high (wrong pump or soemthing else wrong) which you could solve using a fuel regulator

No clue if these suggestions are good I've only had a car for a month now ;)
A.J. van Donselaar

Did you make sure you set up the float correctly? You just can't take the float out of the box and install it and expect it to run correctly. You need to bend the tang on the float to get the correct measurement.
Mike MaGee

Thank you for your responses, the floats are set at 1/8" from the float to the cap as per drawing in the MG manual. I have not thought of a fuel regulator, maybe I will give it a try, what good is money if you cannot spend it on a MG, (just as long as my wife does not find out)

Thanks
Andrew
A.A. McFadden

Please let me know if that solved your problem since I'll have to find a good solution for myself as well :)
A.J. van Donselaar

I had the same problem , and only finally solved it by going to neoprene tipped float valve needles
S Best

Andrew,

I had a similar problem. I suspected it was my aftermarket fuel pump so I installed a regulator, but they still leaked. I ended up removing the overflow tubes I installed and that solved my problem! There doesn't take much vacuum to allow gas to flow past the valves. You didn't say if you had these tubes installed or not, but its worth a shot to remove them, if not just to fault diagnose.

Todd
Todd Alkire

I have replaced the valves twice, both times with SU valves. As for the hose on the vents I never replaced them when I changed over to the SU Carbs.
Thanks again
Andrew
A.A. McFadden

I have the same problem in 67 BGT, except rear carburetter. It's intermittent, so I'm never sure if I've cured it. I've checked and re-checked float levels, replaced float chamber valves and seats, checked fuel pressure (about 3 lb/sq in). I have the same problem in a 56 Magnette, front carb, also intermittent.
I read somewhere (wish I could remember where) that at certain engine revs, a vibration is set up which causes the float chamber valves to oscillate and therefore allow overflow. Has anyone else run across this theory?
I connected the overflow tubing to hoses which go out through the inner wing and dump into the wheel well. Better there than on a hot manifold.
Fraser
Fraser

This thread was discussed between 03/06/2004 and 04/06/2004

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