What causes a 21hp Briggs stration to smoke?

A 21hp Briggs & Stratton engine may smoke due to several reasons, including oil overfilling, worn piston rings, or a damaged valve seal, which can allow oil to enter the combustion chamber. Additionally, using the wrong type of oil or running the engine at an improper temperature can contribute to smoking. If the air filter is dirty or the fuel mixture is incorrect, it can also lead to excessive smoke. Regular maintenance and proper oil levels can help prevent these issues.