ugh...... Now thats a hole!!!!! I'm in kind of the same boat. The PO cut the pipe to make it a straight pipe. If he messed with the jets, I'll have to get some stock ones.
I think the only carb adjustment is an idle adjustment.... but I'm just getting into these GZ's so I'm not sure. I can give you a link to the service manual though.... its on this post.... and it works, I just tried it......
http://www.gz250bike.com/forum/showp...56&postcount=1