I had to replace an '81 BS34 needle valve and seat that hung open on a ledge worn into it. I naively assumed the new would measure the same as the old, so I didn't check the float level. Fired it up and tons of black smoke out that side. Looked at the float and it was set to float a couple of mm too high. Changed it to 21 mm, on a gasket that's compressed to about half its original thickness. Still a small amount of black smoke. Tomorrow will give it an additional mm or two, to account for the thin gasket, which I think will eliminate the smoke. The jets in it are marked stock size. I had no idea you could richen that much with just the float.