At least I hope this is it because it's the only tangible problem I've found so far. I received my replacement leakdown tester and the B&S "L" head engine was the first test to see if it was working properly.
I had tried a crude compression test a while back that showed no symptoms, but with the tester, I located a lot of leakage at the exhaust valve (I could hear a lot of hissing at the muffler).
The symptom was hard to start and keep running, but once the engine was warmed up, it would keep running at 1/2 choke eventually running at 80% power with the choke full OFF.
I can only guess the valve and valve seat expanded as the engine warmed up to where there was enough compression to keep the engine running once it got hot. I can't do the valves for several weeks, but once I do the valves and true the head, the engine should be running a lot better.
My thanks to everyone for their help, tips, and suggestions. I leaned a lot.
Manjo