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MG Midget and Sprite Technical - leaking H1 overflow pipes

After changing the rubber grommets between the floating chamber and H1 Carburettor for fibre I still noticed a petrol smell: Both overflow pipes produce a few (1 or 2 ) drops per minute. I use Viton float needles, for about 18 years, with a spring and a Pierburg low pressure pump (Photo alu one, 2e left). The needles look perfect (without reading spectacles). Any help is appreciated.

Flip



Flip Brühl

Have you checked and set the fuel level? Instructions describe useing a twist drill laid across the underside of the inverted lid to set levels. I forget the size but probably 4mm ?
GuyW

https://sucarb.co.uk/technical-h-type-carburetter-float-chamber
William Revit

That's why I couldn't remember the setting bar thickness! It varies according to the carbs model.
GuyW

Yes, as Guy says, its most likely the fuel level setting, but as the joint between the float chamber and carburettor body is meant to be flexible, I can't see how a fibre washer is going to perform properly.
I would get some new grommets from Burlen. <http://sucarb.co.uk/float-chambers-spares/grommets.html> and check the fuel levels.
Peter Blockley

If your level setting is within tolerance it might help to examine the seat where the needle seals.
I've had lots of trouble recently with leaking needle valves (although admittedly not on SUs - mainly carbs on outboard engines) because of dirty seats. Modern fuel degrades and causes deposits of a whitish hard compound throughout the carb, which can be very hard to see but the smallest bit will affect the sealing of the needle valve.
Your Viton tipped needle looks lovely and clean but the seat must be equally clean. Hope that helps.
Greybeard

I checked the level 4 weeks ago* but did not look for deposits on the seats. It is most probably the deposit. I smell it most if the engine is off and the fuel pump is on. An other thing is that the stationary RPM changes at every traffic light.




*Yes the level is affected by the change from rubber to fiber rings; The original Burlen fiber rings are thinner than the rubber grommet so the float chamber and the level is 1-2 mm higher. So I had to alter the jet adjusting nuts! May be I have to tun them again if the overflow is gone! I ll keep you posted.
Flip Brühl

I cleaned the needle seats with ultrasound and yes; no leaks anymore!
Flip
Flip Brühl

Yay! Well done Flip!
Greybeard

This thread was discussed between 11/12/2018 and 23/12/2018

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