Lawn tractor was running fine and then it started to run rich and engine surges up and down.Black smoke out the exhaust. Replaced spark plug,cleaned rust on fly wheel and mag,set to .12. Fuel line has filter and card bowl clean. Choke works and air filter clean.The main jet on bottom of carb has wires. Is this bad ? Thanx.

Garden - Toro - LX466 22HP Lawn Tractor 13RT61RH244