I bought a 1991 ZX600 Ninja in October. Slacked off on working on it over the winter and now I want to ride it. I've changed the oil & filter, new battery, plugs and air filter. And besides cleaning it I haven't done much else. I bought the bike for $1200 from a guy that had the bike for 3 years and never rode it, and he said whomever sold it to him the carbs needed cleaning. The idle was rough when I bought it, but now, when I rev it the idle sticks to whatever I revved it to. And when it's not doing that, it stalls below 2000 rpm and at 2000 rpm sounds like its running at 500 rpm. I don't think it's running on all four cylinders. Not only that, but there's blue smoke coming from the vance and hines exhaust, between the header and the muffler sections. I Don't See A Leak! I think it's time to just give up and send it to a repair shop.