Not familiar with the 319- is it two cylinder? If so try removing one spark plug boot while the engine is running. If it dies, that cylinder was doing all the work and the other has an issue. Repeat with the other one. You can learn quite a bit about how they're running just by listening. Then you gotta figure out if it is spark, compression, fuel, etc.
Mower can drive around great on one cylinder sometimes but it is really obvious you've got no power one engaging the mower. G'luck.