Wonder if your needlevalve is not seating properly. Try screwing it all the way in and put a piece of tubing on and try to blow through. If you can, there is at least part of your problem. If it will shut off completely, make sure the engine is dry and put a little fuel in the exhaust with the piston up. Turn it over once or twice and put the battery on. A hard flip, and it should fire and run for a second or two. Get it to do that consistantly, then open the needle one turn and try again. Your problem is that your engine, for some reason, is flooding. So what I am advising is designed to keep the crankcase from getting flooded. If you can keep it from flooding you should be able to start it.