Cooling fins around the heads clean? Coil is my first guess.

Clean - has good spark.

You can test to see if vapor lock may be the culprit by pouring cool water on the intake manifold at the carb, and the carb body including the fuel pump portion of the carb and then see if it will start.
One thing you don't need to do is to apply the choke for a hot restart, that only aggravates the situation.

Try shutting off the gas 15 seconds or so before shutting the engine off. IF no shut off valve, clamp gas line.

Walt Conner

It is possible to have an issue related to the float valve/ fuel pump. Presence of spark doesn't necessarily mean what you think it means here however. At times, the CD that fires thois coil goes crazy hot and fires the coil at the wrong times as well. THough this coil fires both cylinders at the same time, it does little good if it fires in the middle of the stroke....

Tried clamping off the hose procedure. No help. Raining today so to heck with it till next week.

Was bad coil.

So, is this what happened? Shutting down after 10 minutes lets the engine heat soak into the coil and affects the spark. But letting it run all day doesn't affect the coil because the cooling fan keeps it at lower temps?

That is what I would presume is happening as the coil is situated where it is one of the first components to be drafted by the cooling fan air output. Good food for thought.