In addition to what Bruce said, have you checked the fuel tank cap vent?
You are following the traditional start-up process through step 3. However after that it sounds a bit random - you don't know if it is too rich or too lean, and you are floundering around.
If nothing is wrong, it should start at step 3, but mine needs the choke at about 80% rather than half, and the throttle in starting position which is about a quarter. (Both these adjustments are probably required because the carburetor is way too big.) It sounds as if you are flooding it at step 4, then going (correctly) through a clearing procedure to start a flooded engine.
