I had been playing with vintage motorcycles for better he 30 years when I bought the small engine repair run which I thought would be a doddle.
What a steep learning curve.
There are hundreds of books about repairing small engines and most of them are not much chop.
Down here we call them coffee table ( if they are full of photos ) or bedside ( no pictures ) books.
Lots of information so general in nature as to be useless.
The best books are the John Deer Technical manuals as they tell you how the bits work and how to test them and what order to test them.
Most technical college libraries will have them and some are available from the web.
However GOOD & CHEAP are mutually exclusive. It costs money to write good manuals.
Other than that, You Tube is good once you sort out the shaved monkeys with a camera from those who actually know something.
Taryl Fixes All & Donnyboy87 are very good, subscribe to their channels and run through the entire play list.
A lot of parts suppliers also have videos, e-eplacement parts, Jacks small engines.