I found that the easiest way to start the lawn-mower is to remove the
air filter then squirt a few strokes of engine starting fluid over the
butterfly valve. I could start my old lawn-mower after a few pulls
even it has been sit outside for several months.

Engine starting fluid can be found in most auto part store for couple
dollars a can. One can should last...for years. "WD-40" also works
too.

It works everytime for me and my neighbor.

Good luck.