17 hp Murray Mower Won't Start?

My Murray 17/42 Ultra riding lawn mower with a 17hp, ohv industrial Tecumseh engine needs gas poured directly into the carburetor for it to start. Once it fires up, it runs fine, but even after I let it run for a few minutes I have to take off the air filter and do it all over again.

Suggestions on what I need to do to fix it? I got it on trade and the guy said he was told it would cost like $40 to fix, if he took it to a shop, but there aren't any shops near here that I can take it too. I don't mind changing parts, but I have never had a Tecumseh engine before. I don't know where to even start.

By Bill L