1. Park the mower on a level surface and turn off the engine.
2. Locate the carburetor. It is usually located near the top of the engine, near the air filter.
3. Clean the carburetor. Use a carburetor cleaner and a small brush to remove any dirt or debris from the carburetor.
4. Check the carburetor gaskets. Make sure the gaskets are in good condition and are not leaking.
5. Adjust the idle speed screw. Turn the screw clockwise to increase the idle speed, and counterclockwise to decrease it.
6. Adjust the mixture control screw. Turn the screw clockwise to lean out the mixture, and counterclockwise to richen it.
7. Test the mower. Start the engine and let it run for a few minutes. If the mower runs smoothly, the carburetor is adjusted correctly. If the mower does not run smoothly, repeat steps 4-6.
Here are some additional tips for adjusting the carburetor on a 21hp Briggs and Stratton mower:
* Make sure the air filter is clean. A dirty air filter can restrict airflow and cause the engine to run poorly.
* Use the correct type of fuel for the engine. Using the wrong type of fuel can damage the engine.
* Check the fuel lines for leaks. A leak can cause the engine to run lean and damage it.
* If the mower has been sitting for a long time, it may be necessary to drain the fuel tank and replace it with fresh fuel.
