Got junk in the fuel tank and apparently into the carb. We took it off, tore it down, and soaked it. Cleaned out the tank and the filters, and put it all back together. It will start and idle, but its running very rich. Big black smoke rolls when you hammer on the throttle. We tried adjusting the air/fuel mixture screw..but you can turn it either direction without any change in the idle. You can almost take it completely out with no change. We took it back apart, resoaked it, ran thin wire through the tubes, and put it all back..same thing. Changed the plug again...we are stumped at this point. Its in pieces right now in the bay of the FD, any help would be appreciated.