Instead of paying for textbooks a better idea would be to search the web for specific service manuals. 90% of small engine service manuals are available in PDF form. All you need to do is use your search engine and start looking. I suggest the first two you look for are Briggs and Tecumseh L-head engine manuals. Both will give you a basic understanding of how engines work and basic troubleshooting procedurers. I'm not going to post exact sites, because you will learn faster how to accomplish this goal. Researching on your own is just like troubleshooting an engine, even Green Industry & Equipment research engineers will agree with me on this.