35 year old carbs can have problems. In this case, the (a) problem was “sticky float valves” Also, lots of rubber gaskets and O-rings were getting hard.

So I got a carb rebuild kit from Amazon. I didn’t use the needles or jets, because they’re unlabled and wrong (based on measuring). I thought, “How bad could the floats be?”

Well, it turns out, “unusable without modification”

Can you see what’s wrong here?

How about now?

Yes, the body is so long the valve never actually closes. The valve bottoms out on the body before the cone touches anythings!

That explains why the bike just dumped fuel out everywhere.

So, I trimmed 0.030" from the top of the valve bodies: (video link)

Deburred:

That’s better:

It’s yet to be seen if the floats have the right boyancy (how do you measure that?) but at least now there isn’t fuel just pouring out.