Small Engines (Lawn Mowers, etc.): type of engine, craftsman 917, spec numbers

Question
Hi Paul!! I have a craftsman 917.256510 lawn tractor with the B&S 28N707 Type 0171 01. I have some smoke and back fire issue with my lawn tractor and went online to look for answers. I just wondering that my engine model is 28n707 but there're many different type. Is there any different between type 0171 and type 1026, 0526, and other different type out there.........I'm a handy man but never try to fix any engines, i do all the routine maintainent on my car and i wish to start a new hoppy to fix and understand small engine. Do you have any website or text books that show how to fix my engine model.
ps anything would help

Answer
The second set of numbers, the "spec" numbers are the small difference between each engine.  The spec # denotes everything from fan shroud color to charging system amperage to crank diameter, key size, thread of crank etc.  Generally there is 1 basic spec and about 200 different configurations.  Briggs offers a great small engine manual.  Your dealer can order it for you.