Small Engines (Lawn Mowers, etc.): oil pan gasket change, camshaft timing, pan gasket

Question
the patient is a craftsman 6.6 Eagel-1 model # 917.377300 serial # 022497M  011885. oil pan gasket was leaking the engine ran fine.
the pan gasket was replaced and now the engine backfires and will not start what was done wrong.
Thanks

Answer
Did the camshaft timing get out of place?  Did you check the flywheel key to see if it is sheared?

Do you have the engine repair manual?

http://www.smallenginesuppliers.com/html/engine-specs/tecumseh/Tecumseh_L-Head_E

Eric