Boit,
You have a slide that is worn. Mikuni puts a very fine layer of
teflon on the slide and given the clearance in the slide bore the
slides wear quickly. You can get a new one from Sudco, I just
got my replacement, I believe it was ~ $28 to my door.
http://www.sudco.com/
I made a slight modification to my existing 33 Mikuni, that puts
more preload on the spring, which keeps the slide from hanging
up. I am going to hold off replacing my slide, until this mod no
longer works. I posted a write up on Thumper Talk iin the KLX
Forum, in case it may be of interest.
http://www.thumpertalk.com/ubb/Forum27/HTML/000004.html
BTW this is fun carburetor to disassemble, you might want to make
notes, use a digital camera, or a camcorder and watch out for that
pumper cylinder and spring. They both like to fly out, real easy.
Here is a URL with a diagram of the 33mm Mikuni Pumper Carb;
http://carbparts.com/mikuni/tm_expl_view.gif
Hope this is of some help MC !!!