Hello, It sounds like a safety switch. The most likely choice is the neutral safety switch but it doesn't make sense that sitting cures the problem. You can try shifting the lever to forward and back to neutral and try starting. You can also try shifting while turning the key (difficult but possible) and see if you can find a position where tries to turn over. The other possibilty is that you have a starter going bad or enough corrosion on the battery that the voltage drops when it gets hot. You can clean the battery connections and if it is new battery lightly sand the post for a better conection.This next part sound strange but turn the engine by hand counter clockwise until it stops, you are taking it off compression and it will have less resistance to start. It may be a problem that needs to get worse before it can be properly solved.Thanks Tom
I cleaned and sanded battery terminals when I installed new battery. Should I do the same where cables connect to frame and starter? The connection at starter looked aged and tired but didn't have acid junk as forms at the battery. I left it alone. Can't easily see where the ground cables connects to frame.
Where do I grab it to turn the engine counterclockwise?
I doubt the problerm is on the starter end. I beleive your flywheel screen is not covered and you can actually turn it with the flywheel screen.