Usually I will try to start them out right like you have been, maybe use some carb spray. If it still fails to start and I have verified that I have fuel and spark I screw in a new set of NGK's not that Champion garbage, If the spark is small I make sure the points are right as well as the condensor. I never use starting fluid, I have a few motors that have been blown up by using this stuff (starting ether). Then if I can get a fair start up then I go through the carbs.