Hi Doug,
My favorite mower, absolutely amazing machine, I have 4 of them here at the moment, but I have had 2 in the last couple of weeks I could not get a kick out of,gave up for a couple of days then for no reason they both started easily. Don't continue pulling to the point of hurting your shoulder try drill starting it. Plug being dry indicates either carby not working or seals not sealing. Give it a light spray of starter fluid in the plug hole and see what that does, that is my first starting point, it helps me tell if it has been straight fueled.This puts fuel above the piston so it is not relying on the carby or seals to work. Try several plugs just because it sparks doesn't mean it will fire under compression. If you get a pop out of it with the starter fluid then I would look at doing the carby mod that is the only way I can get 98% of them running properly