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MG Midget and Sprite Technical - Fitting new rubber washer to float bowl from jet ?

I need your foolproof / best method for fitting new rubber washers to the pipe end of the jet to the float bowl. SU H2 carbs on 1275 engine.

(Some of the worst design I have seen...)

Took them off to check for any blockages (none), replaced and leaks galore. New rubber washers required - any seller recommended?
Tim Carter

I assume you mean this.

No trick to it.

You just slide the rubber o ring over the pipe in the order shown here.

As you tighten the brass bush, you compress the o ring, and that creates the seal.

Make sure you are pushing the seal onto the pipe far enough, to allow you to insert the pipe far enough into the bowl.

Otherwise you will not compress the o ring as you tighten the brass bush, and it will leak.

Have you removed and if so, refitted the brass insert? #4.

anamnesis

OK, I get the method, having thought it through, was going to attempt similar.

Hmmm,

brass insert (#4) will have to check if these are there...don't remember having to fit them when new ( new jet assemblies, 4/5 years ago)

Any ideas on where to get the O rings (#3) or their specification ?
Tim Carter

What happened to the originals?

You may find them still in the fuel bowls.

anamnesis

You could try this.

https://www.ebay.co.uk/itm/145955067807

Although I don't think there's anything wrong with the original system.




anamnesis

Or you can buy the original o ring and washer etc from Moss.

https://www.moss-europe.co.uk/en-gb/carburettors-5-twin-1-1-3-4-7-hs2-su-s-sprite-i-ii-sm--20--03--02

O ring £1.39 plus postage.

anamnesis

The original correct O ring was square sectioned, though I've no idea if that was significant. What was important was not to over tighten the brass nut. It's little more than finger tight, maybe + 1/4 turn
GuyW

Yep. Only ever needed nipping up.

I think the design was fine. I never had a problem with it, and it was employed for a very long time across a range of SUs.

You can buy the insert (ferrule) too if you've lost it/them.

https://www.moss-europe.co.uk/en-gb/carburettors-5-hs2-su-sprite-iv-midget-iii-1967-74-sm--20--03--03

Ferrule £1.39 too.


anamnesis

"The original correct O ring was square sectioned, though I've no idea if that was significant."

I would think that is significant, although I'm not a fluid dynamicist.

Brake caliper piston seals are also square sectioned.
Dave O'Neill 2

Ferrules in place already.

Thanks for the links, tempted by both!

Off to do a refit then see how much petrol hits the garage floor this time!
Tim Carter

All back together, connected up to fuel pump, no leaks :D

Thanks all for help and guidance.

Will probably buy the O rings AND the metal olives for backup in the future.
Tim Carter

Now you can get back to your main problem thread, and solve the mystery of why the engine loses power and splutters.

anamnesis

And a reminder to self, don't forget to fit all three springs back onto the carb linkages, only did the accelerator cable one. The engine revved up like a jet engine on first start ;)
Tim Carter

I'd back an o-ring seal against a ferrule any day of the week.
And having used e10 for 12 years with no issues on the o-ring, that is a red herring claim in my experience
Paul Walbran

Another piece of advice, don't try to do this with the carbs on the car, you just cannot see what you are doing, and getting spanners on is also tricky.

As an aside, after all the fettling and checking, my carbs are now out of tune...one is an Bb the other is a C# - need to get them both back to C.
Tim Carter

I love a good story--tell me how did your carburettors get different needles to each other--was it like that when you had your missfire issue- A BD needle is way leaner than a C it'd be out of balance like that--
William Revit

It has been awhile since I played an instrument and could read musical notation but recognised Tim's comment as a bit of a joke I think, Bb (B flat) and C# (C sharp), the carbs are a bit out of tune.
David Billington

What would you think if they ran out if tune
Would it splutter and cough and then die?
Lend me your jets and I'll start the engine
Then we'll see if it makes the thing fly

Oh now I'll have a stab at anything
Mm now I've just about tried everything
Mm so I might as well try anything

😆😆.

https://youtu.be/HI865Eo7-Yc?si=WDJsTLMljP-ECxQG

anamnesis

This thread was discussed between 05/10/2025 and 07/10/2025

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