Morris Minor Owners Club

My mixture seems to be too rich. I can start the car from cold with virtually no choke. Plugs are black and I have a sooty exhaust. Once running from cold pulling out the choke kills the engine. It seems pretty clear my mixture is too rich. Adjusting nut is almost right at the top.

I rebuilt the carb (an original H1) because it was leaking. I found the leak was coming from the brass washer marked in the following picture:



As this is just a slim brass washer it didn't seem to be sealing the jet at all. I replaced it with a rubber O Ring washer and it fixed the leak. But now wondering if it has resulted in an uncontrollably rich mixture?

Any thoughts would be welcome. Should I try a leaner needle? If so, how do I know what my current needle is?

The standard needle for an H1 carb on a Series II should be a GG. If you remove the needle from the piston, there is a grub screw which clamps it in, the needle code is stamped on the shank. You may need a magnifying glass to read it.
It is important that the base of the needle is level with the bottom of the piston.
An incorrect needle is unlikely to be the cause of your rich mixture on tickover since there is very little difference between the 1st dimensions on most of the 090 size needles.
Rich running is likely to be caused by wear to the needle and jet, petrol is quite abrasive, which is why you have had to screw the mixture nut right up. The correct adjustment should be about 2 turns down. Have you replaced the needle or jet?
Most of the leakage problems are caused by the cork seal below the washer, also check the fuel level in the float chamber

The cork is supposed to be compressed by the conical shaped washer - I think the thin brass washer is just there to protect the cork - doubt it would be source of leak. the whole lot should be clamped up tight - but not so tight the jet can't move. jet could be worn - look at the top - should be round hole (90 thou) - not oval! needles rarely wear - but you 'could' set it very slightly proud of the piston to allow weaker mix to be obtained. most likely of all though is fuel level too high because needle valve leaking and/or float punctured/set too high. When engine running normally - it uses the fuel so no problem - but when idling - the level goes too high and floods over the jet - causing far too rich mix and v possibly your 'leak'!

Thanks for the replies folks

The leak was not on the outside of the jet body (sealed by the large cork washer and conical metal washer) but inside this jet body, the area protected by the two small cork washers.

In any case I think what has happened is that the jet itself is now a little too low in the body of the carb, meaning the needle is not seating fully when at it's lowest point. Will strip her back again this weekend and investigate. For good measure I will order a few needles to try if this doesn't work.

Will also check the float chamber BMC - What exactly am I looking for here? How do I tell if it's out of whack?

Cheers

Take the bell off the carb - switch on ignition and let the pump fill the chamber - it should click a few times - then stop. You should be able to see the fuel about 1/4" below the bridge in the carb. If it's higher/pump keeps ticking/fuel overflowing - then there's the problem.