How does the "hot" spark compare to the "cold" spark.

When under compression, it's harder to generate a spark then when the plug is out of the engine.

I'm no mechanic.

1) I ran the mower 30 minutes or so.
2) I let it sit minutes or so
3) I took black cap off plug
4) I put spark tool thingy - one end on actual plug, other end on black cap

5) I pulled cord
6) daughter said she saw spark each time I pulled
7) after 20 more minutes, it started up again.

So, I am not sure how to answer your hot/cold spark question.

The dealer thought it could be a compression issue...if I saw spark at all.

I am just trying to figure out if I am wasting my tim etrying th enew coil? I am not even sure whats involved in replacing it.

If you are going to check the quality of spark when cold, you don't run the engine first!

Compare cold vs hot when the problem occurs.

What am I looking for? How does this impact whether or not try the coil.

I plan on doing grass again. I will note the spark before running and again a half hour later.

My question is, if the spark appears more vivid when cold that when hot and not re-starting, does this mean it could be the coil? Should I try to replace it? Is it a waste of time?

Or is it a compression issue?

Ok, I checked, spark on cold engine more intense than spark and hot engine. Starts cold and runs fine. Once hot, wont restart until it cools down.

Coil issue?

Have you checked the flywheel key? A damaged Flywheel key will throw the timing off and can make an engine hard to start when hot.

The key is pointed out here by the red arrow.

This post was edited by hippy on Wed, May 7, 14 at 10:34

I will have to take a look. Is the pic a shot of a damageed one? (so I know what to look for) Perhaps I can post a picture...might need a day or two...

...and btw, if it matters, the spark was yellowish in each case.

Is the pic a shot of a damageed one?

No it is good.

A sheared one will look something like this,

Orange is a weak spark. You want a blue spark