Mower won't start unless I put gas in the spark plug well
I have a Briggs and Stratton 4-cycle, OHV, self-propelled mower. It is several years old, we just got it from a friend. It worked the first few times we tried, then just woudn't start. I changed the spark plug and air filter. Still nothing. Then I pulled out the spark plug and put a little bit of gas in the well. It started and ran like a champ for an hour while I finished the lawn. I believe this is a carburetor problem, but don't know for sure and I am a novice repair guy who wants to learn how to do all this myself. What do I need to clean/fix/replace, and how do I do it?
Thanks so much.