Hi jerry, in your notes above you state take the water pump impeller off, then start the engine momentarily, Why?
I agree with all else,
Plus after removing all old fuel, take out the fuel line in the tank, check the strainer at the bottom, and the anti-siphon valve for crud, or water. Then all your fuel lines, and filters. After 15yrs, you should probably take out the spark plugs, and spray some motor oil into the cylinders, then put the plugs back in (to be changed later). Then crank it over with the coil wire off to circulate the oil. The First thing you want to do after that, is put the coil wire back on, the garden hose, and ear muffs on, then turn on the water, AND Check for any leaks before starting, if none try starting, and running the engine up to operating temp at low speed, watch your gauges. You might need to take off the flame arrestor, open the choke, and spray some starting fluid into the carb (only a little) if it's stubborn starting?
Another thing to check is your fuel tank vent, make sure it's clear, and no wasp nests in there?