SHcooter.com

You are getting too much fuel. It's running rich because of:
1) choke is stuck
2) air filter is clogged
3) carburetor float has a hole and is filling with gasoline
4) The engine is worn and oil is getting into the combustion chamber (4 stroke)
5) Too much oil is being injected into the engine (2 stroke)

If you can't troubleshoot this yourself, take it to a trustworthy shop. It won't be expensive to fix unless it's a 4 stroke with a worn engine.

Clean the spark plug and also carburetor time to time. also check the fuel tank that it is clean or not.check the oil cumbustion . Is it going less or slow to the engine?

What's the make, model, miles, modifications, etc....?