I had replaced the coil and gotten spark back to the plug but it still
wasn't starting. While the plug looked good, I still went and bought
another. The 'old' plug was indeed one of the flavors that has the resistor
to cut down EMI.

When I put the new plug in it started. However, it ran rough and very
finicky. When I started using it it would stall very easily. I got about
30 minutes useage out of it and had to start it about 15 times. Each time
it got progressively worse and finally it wouldn't start at all.

As I was putting it away, I noticed there was some oil dripping onto the
deck that appeared to be coming from somewhere around where the carburetor
attached to the engine. (I am very sketchy on this as I was in a rush and
haven't gone back and looked more closely.) I had not had the lawnmower
tilted or flipped that day.

[I still need to check the flywheel key as sugested by Stormin Mormon.]

[Q: If running the oil/gas mixture in the 4-cycle fouled my valves, could
pulling the plug and filling the cylinder or spraying lots of carb cleaner
in the plug hole (while ocasionally rotating engine shaft to insure the
valves were open sometimes) at least partially clean the valves?]

On a related note and a different thread, I bought a lawnmower from somebody
else here that was sold as 'not running'. I only paid $10 for it and was
hoping that maybe between the two I could put one together and have a
running mower. It however sounds real sick when I crank it and was probably
$10 wasted....