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MG Midget and Sprite Technical - Fuel overflow

I have just replaced my fuel pump with a new SU electronic type and fitted a Malpassi filter and regulator . I have now developed a fuel leak when I switch on the ignition forming a small pool on the rear float lid (HS2) . I presume nothing I have replaced is causing excessive pressure , what are the likely causes please ?
Mike Fairclough

Try tapping the lid of the carb float bowl (chamber) with the handle of a suitable sized screwdriver a few times with pump running and see it that clears it.

If not it might be a bit of muck in needle and seat that needs blowing out, or otherwise removing.

Worst case bypass the filter as a check, SU pump *should* be at correct pressure so pressure regulator not needed (as I've been told many times over the years).

Or remove connector to filter and switch pump on to measure output about a pint a minute or ratio of, steady flow not too much pulsing or air bubbles.
Nigel Atkins

Thanks Nigel I will try the tapping , needle valve clearing and see how it goes. I know the regulator is strictly not necessary but wanted a filter and seemed the Filter King was the best option .
Mike Fairclough

I'm all for trying easy quick and simple stuff before moving on, often as that's all I know.

It's each to their own Mike, I do think a filter is a good idea (mainly so that I can see if the petrol's made it that far without getting my hands dirty).

I'm also not a big fan of the (present) SU company or their pumps, I think you pay extra for the brand name, but I'm biased because I've had to deal with the miserable sods there and I'm not alone in that opinion, I think as they're the only source of some bits (not as well made as previously) they have a take it or leave it attitude, but I could be wrong.

Let us know how you get on.


Nigel Atkins

Tapping the carb with a screwdriver handle or soft faced hammer was well demonstrated in that two cylinder A series engine video. Carb was overflowing but a few light taps on the float chamber whilst the SU pump was running and it instantly cured the problem.
GuyW

Just an update and thank you . Unfortunately tapping the top didn’t do the trick . I took the tops off and removed the valves and cleaned them and the seats up . Felt a ridge on the valves so could probably do with replacing. Anyway all back together and touch wood no leaks so far so fingers crossed will be ok until I do a proper carb rebuild .
Mike Fairclough

Well done Mike, thanks for reporting back.

Get Viton tips if ordering new.

If you're going to be doing the carbs later take my tip and buy the SU type tool kits, I didn't and wished I had. The mixture nuts can be a bugger to adjust by fingertips or conventional spanners. The seat is I guess a BA size so the kit socket is a better fit and the link finger lock nuts are (2?)BA. If you need it don't bother buying SU's 1275 throttle linkage lever as it's not correct despite what they advertise - and if you feel too blessed and happy with life give SU a ring to restore the balance. 😊
Nigel Atkins

This thread was discussed between 09/04/2021 and 10/04/2021

MG Midget and Sprite Technical index

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