Hi jm, this is Dave, the Small Engine Doctor. Start with taking out the plug and spraying some carb and choke spray in the cylinder and rotating the engine with the starter rope, slowly. then pull it fast to blow out the excess. Do this a few times and then put in another new plug and see what happens. Theres a possibility that you've built up some carbon on the valves and its kind of screwing things up in there.
Please send me the model and type number of the engine so I can look up the drawing and help you further if the above doesn't work.
If you are pleased with this answer, you may go ahead and click on the "accept" button. I will still stay with you until we get this "puppy" running. Please let me know how you made out!! Sincerely, Dave