I have an 85 cb450 nighthawk that runs to rich. I have gone through the carbs and cant find the problem. The jets are stock, floats are not adjustable and measure good, and I replaced the float valve needle. The pilot air mixture screw is set to the leanest setting and still the bike runs rich. It starts without choke even on cold mornings, gets poor gas mileage(25mpg), and the plugs look sooty. The air filter is new. Bike runs good and if not for the symptoms I mentioned you wouldn't think there was a problem from ridding it. Does anyone have any ideas on what i should look into next???