I'm having trouble with a 1988 Bayou 300. It was in pretty tough shape when I got it. It burned oil and needed exhaust. I rebuilt the top end of the motor with a .020 piston, new valves, guides and seals. I got a cobra exhaust pipe and rebuilt the carb. The problem I have now is it runs way too rich, black smoke out of the exhaust, and it will soot up a plug in a matter of minutes. I have reassembled the carb about 30 times and cannot figure it out. I even put all the old needles and jets back in, but nothing seems to help. I thought the aftermarket exhaust could be the problem, but I thought that usually made it run lean? I was thinking about getting a different size pilot jet, but I don't understand why it would be different from stock. I start with the air screw and 2 1/8 turns, but it doesn't seem to make a difference which way I turn it. Anybody have any ideas ?