I fix motorcycles as a hobby, it was also how I learned about engines when I studied my first degree in Aircraft Engineering.
In the 13+ years of restoring motorcycles, I've came across many motorcycles with dodgy repairs. Typically by tinkerers who thought they knew more than the designer. Some of the excuses I've heard are amazingly ignorant.
It's fine having a hobby but if you are going to repair a vehicle, then make sure you do it properly. A dodgy repair can cost someone their life, so you gotta do things properly. Online forums can provide good and bad advice.
However, this book provides sound, solid, credible advice in a way that most enthusiasts can understand.
The book covers topics such as the Cylinder head, exhaust, carbs, ignition, and lubrication. It provides a wealth of knowledge for tuning such systems.
Get this book if you are serious about tuning your vehicle or want to learn more about engines.