I spent some more time trying to figure this thing out and now I find
we need to backtrack again.

I tried the test again where you crank the engine with finger covering
the spark plug holes. When I cranked it using the starter I thought I
felt puffs and suction from both cylinders. This time I had my helper
just turn the flywheel while I had fingers over the holes. I got a got
puff and suction from one cylinder. On the other cylinder, however, I
got a puff, but little or no suction. So maybe Ether's original
thought is right about a valve problem? What should I do now?

Ether Jones wrote:
Don Young wrote:

That is a good way to test the compression. However, a compression test is
not of any use to diagnose a slow cranking problem.

Read the rest of the thread, Don. The OP stated that the engine slowly
stalled out while his son was mowing the lawn. Then when he tried to
re-start, the cranking was slow. We're trying to determine if the two
are related. Very few single failure modes could cause both problems.
But a valve problem could cause both problems. If compression differs
greatly between the two cylinders it could indicate a valve problem.
So it's worth checking.

Abnormal compression is very rarely too high

The compression doesn't have to be "too high" to cause a cranking
problem. If the exhaust valve is stuck shut in one cylinder, for
example (broken valve stem?), the starter motor has to work harder
because it's compressing on the exhaust stroke. This would cause
slower cranking.

and if the compression is too low the cranking speed
would be greater. It is possible for excessive fuel or oil in the cylinders
to cause slow cranking but it should blow out if you remove the plugs and
crank the engine.

I would suggest that you remove the plugs and check that the engine spins
over easily.

He already did that. It's described in an earlier post in this thread.

If it does that but turns over too slowly with the plugs in and
9.5 volts across the starter, the starter is very likely not performing
properly.

That's the current most likely answer (for the cranking problem) based
on the tests run so far. But before he runs out and buys and installs
a new starter motor, it was suggested that he rule out a valve problem
(which could cause the engine to crank slower, and would ALSO explain
the stalling described in the original post).