The left carb is leaking badly. I read all the way through Snow Bum's ramble and came to this:

" it is not uncommonly simply an old worn needle tip that has a slight groove in it, and should be replaced."
https://bmwmotorcycletech.info/Carburetors-that-piss.htm

So I ordered a float needle, but dumb question. Nowhere can I find how to put in the needle. I think it just sits there above the tang between the floats. Do you have to pull the knurled pin and remove the floats?

I tried the Bing Dance #1 – messing with the float on/off to try and get any particles out. No luck. Still pisses badly.
Also, replaced the cork gasket on float bowl.

Interestingly, I can just run with right hand petcock open (left closed) and it doesn't leak. I don't understand that.

Thoughts or a better article on float needle installation?
thanks!