Gunter is right. The needle is tapered downwards so it is narrower at the bottom. That means if you undo the nut, you are moving the jet lower on the needle so there is more space around the needle to let fuel through = richer.

It is a bit counter-intuitive because generally one is working from above the nut, so screwing it up tighter feels as though your are undoing it. You have to visualise it from below to get it right.

Hi David,

these are the tools you're looking for:
www.stevens-shop.de/shop/MG-B/Kraftstoff...-Vergaser::3462.html

Very useful, especially to synchronize the twin-SUs.

As for weak and rich. I recall that turning the nut out of the carb means richer and turning it in means weaker.
Günter

Armed with the workshop manual & car handbook I set out to adjust the carbs. Car runs quite smoothly, but is running rich. No hunting, but sooty exhaust & it starts with almost no choke! - a friendly Garage checked the CO2 reading & got 6 to 7 instead of the 1 to 2 that he expected, My old TR3A used to be around that too.
Now all the books say is "screw the jet adjusting nut up in order to weaken the mixture". My brain is fading, so this means screw the nut nearer the carb body? The nuts are "not easy" to get at & won't "screw up" by finger, I recall there were SU jet adjusting spanners around, but on flea bay there is nothing specific for an H4 1.1/4. Anyone know the across flat distance? I can modify/shorten an old O/E spanner to suit if I can't find a real one.