Third cylinder is missing and it is running rich?

If you have a misfire the system thinks the engine is running lean so it will increase the fuel input to its max. So, we need to fix the misfire and that part should go away. Let's remove the spark plug for inspection and replace it if needed.

This guide can help:

https://www.2carpros.com/articles/how-to-change-spark-plugs

If that does not help let's do a compression test.

https://www.2carpros.com/articles/how-to-test-engine-compression

This guide can help as well:

https://www.2carpros.com/articles/engine-misfires-or-runs-rough

Please go over these guides and get back to us.