Stan...First, unless it is very cold, you really don't need too much choke, certainly not 5 minutes worth. If I understood you correctly, it sound like you are choking it too much.
When I start a cold engine, I choke it full, but after the engine starts, I reduce the choke as quickly as possible to no choke at all. A minute or so has been more than enough for me. Lean out the idle as much as possible...that will help burn off the carbon and keep the plugs clean.