My 20 years old Murray 425600X8A ran ok before. It went bad after a small engine shop performed the tune up and changed to a mulching blade. The tractor exhaust pipe spitted gas when started, and blew a huge of white smoke then halted. The shop took the tractor back and suggested to get the engine rebuild. I don't want to spend more $ and took the tractor back. Found the fuel pipe to the carburetor was loose so I plugged it back. It is a Briggs Stratton model 31D777 type 0235E1. Ordered a fuel line clamp and try to fix it myself. I plan to rise the cutting height since the shop lowered it before. Any advice/s helping me to diagnose/fix the problem/s will be appreciated.