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MG MGB Technical - Rough running

Car was running a bit rough on inspection looked like fuel had running down the side of one of the float chambers, I suspected the grose jet might have dirt in it or faulty but it all seemed OK. I then found the plastic float was full of fuel, can’t see where it’s getting in but I would think this is the problem, got to wait for a replacement now.
Trevor Harvey

Yes, if the float doesn't float, the needle valve can't shut off and the chamber overflows. The mixture from that carb will be over-rich too, hence the rough running.
Mike Howlett

Just goes to show how difficult it is to help someone when they ask why is my engine not running very well, to have a faulty float was not what I expected to see.
Trevor Harvey

If it was overflowing fuel would be pouring onto the ground and the pump chattering away. Probably just lower than it should be raising the level in the float chamber and jet so upsetting the mixture.

Float level is supposed to be pretty important, early floats (and Stay-up, which can still sink ...) had a metal piece between float and hinge that could be bent, but all-plastic that were used for many years were fixed. All you could do with those (short of heat I suppose) if the fuel level was too high was to put a spacer washer under the valve, nothing if it wasn't high enough.

Never understood why Grose called them 'jets'. From what I read a while ago the company was sold, the new manufacturer cut corners and they were not as good as traditional valves. They have been Viton-tipped for a while, I've had no problems with those.
paulh4

Replacing the faulty float seems to have cured the rough running problem, I couldn’t hear if the pump was clicking away as apart from being a bit mutton the cars is quite noisy. I have owned the car for 19 years and grose jets were in it when I purchased it with no problems so I can’t complain about them.
Trevor Harvey

Let me take a wild stab here - a bit "mutton" - Mutt and Jeff, deaf? Rhyming slang? John.
J P Hall

As no doubt have others here, over several decades I have serviced hundreds of carburettor, but I have never found even one defective new genuine SU needle valve, either pre- or post- Burlen, of either the brass tip or Viton tip type.
I have seen original ones worn out and leaking after a very honourable mileage that had worn a step in the tip, and many aftermarket needle valves that simply weren't up to the job and leaking.

Regarding the plastic floats without a tang, I have found that fitting a new float and new float pin consistently brings the float level right without any need for adjusting washers provided the pin is still a firm fit into the lid as original.
Paul Walbran

Yeh, jP Mutton you’ve got it, quite a common saying here still in the old country especially with the older generation.
Trevor Harvey

This thread was discussed between 14/08/2023 and 17/08/2023

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