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MG MGB Technical - leaking float chamber and fuel fallback

Hi folks

My '69 bgt has a leaking float chamber and I am getting fuel fallback overnight. I presume that this is down to a non-sealing needle valve? Are those ball valve replacements any good? I've also bought a set of float chamber lid gaskets too. Any advice would be greatly appreciated. Cheers

r j symons

If I understand you correctly, the fallback means the float chamber leak leaves it empty after you have been stopped a while and there is furious ticking under your seat when you restart ? The answer is to dismantle and clean the carb thoroughly. On the question of the valve, they used to give probs even when new so, in the early days we changed them automatically for an aftermarket alternative.
R Walker

A non sealing float chamber valve won't empty the float chamber when stationary. It will however cause flooding when running which will lead to erratic running, particularly at idle. Lift the bonnet while the engine is running, if it's flooding you will notice the fuel smell and see the over-flow pipe(s) working. AND if you park on a steep slope, the higher carb can put fuel in the inlets and the bores. If the fuel level is dropping over night, it could be evaporating due to heat soak if your heat shield is missing or faulty, or fuel could be leaking past the seal on the jet fuel pipe where it emerges from the bottom of the float chamber.
Allan Reeling

Thanks for your replies, guys. The float chamber lid gasket is definitely leaking, and the overflow is also working. But I'm also getting the fuel loss when not running so it may be that seal on the jet fuel pipe as well then, as the heat shield seems fine.
r j symons

Double check where the jet tube enters the base of the float bowl. These are notorious leaking spots and the packing gland washer must be installed correctly or leakage is a certainty. RAY
rjm RAY

The gasket on (presumably) an HS (with the side-mounted float) only stops leakage under sharp cornering and acceleration/braking as the fuel slops around.

It's normal for the float chamber level to drop after switch-off, and isn't in itself an issue even if they completely empty, as my V8s do after switching off on a hot day, they simply refill when the ignition is next switched on. However if there is a leak from the jet pipe, or the chamber is cracked, then that *is* an issue as fuel will be leaking from it very near the exhaust all the time you are driving.

Personally I'd avoid those so-called Grose Jets (jets?) with the ball valve, at one time people swore by them, now they swear at them. Manufacture has changed and they leak. The manufacture of the original needle valves has also changed but for the better, and the Viton-tipped ones made now are fine, although personally I've never had a problem with the brass ones over 40+ years.
PaulH Solihull

"in the early days we changed them automatically for an aftermarket alternative."

They were very similar in design, different materials and better made. The Grose jet has come along more recently. There have been problems with it.
R Walker

This thread was discussed between 05/12/2012 and 07/12/2012

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