When I taught small engine repair, every student had to completely teardown, measure, and reassemble an engine in one semester. Along with classroom work there was no better way to learn how an engine works. Many of the engines did not run at the end of the semester, because the parents didn't want to stick any money into it. No problem, as the students understood how it was supposed to work. Also, helping other students troubleshoot their engines was a great team learning experience. I would start with a Briggs or Tecumseh, as their repair manuals are available in PDF form on the Internet for free. Once they understand how each part works together and alone, you will be a better troubleshooter down the road. This is one lesson that persons on this forum need to learn before attempting to work on their equipment and posting questions.