Buy service manuals of the engines you're interested in?
In addition to what spv suggested about previewing books online, you could try checking your local library as well. I'm not sure if the library I go to is the norm, but they have service manuals, general small engine and automotive books, specific books on mowers, chainsaws, outboards, electrical systems etc. Might be worth checking out, and if you see something you like you can always buy it for future reference