If I were to assume that the bike used to run fine and just hasn't in a while, I
would not focus on the carb internals. Yes they might need a good cleaning and
blowing out but I think the problem might be elsewhere.
Since the bike is from 1990, I might suspect vacuum problems. Hoses may have
dry rotted by now. Vacuum problems will definitely affect anything beyond idle.
Arthur
Glendale area, Calif
ZX900A2