if it is popping back through the carb, you've probably got a stuck intake valve.. but I would be more likely to suggest removing carb, re-clean it, check gaskets to intake, and look in the intake port and see if valve moves while rolling engine over.
Electric starter is only designed to be run for up to 15 seconds continuously, and a 1-2 minute cooldown, as an absolute minimum - do not crank more than 15 seconds.. doing otherwise, you'll end up needing a new starter
There is only ONE throttle on this machine - the other "throttle", I suspect, is actually the choke. (and it is open, right?)
Also, you could have a mouse nest in the blower housing, and mice chewed up your coil wire or ground wire or both. (you'll need a new coil if they chewed up your coil wire, though Ive seen some people have success using silicone RTV gasket sealer to re-insulate it... )
-If it is a valve and you don't wanna pull the head, This stuff works wonders (I just used it today, for the third machine in the last 6 months, and yet another sticking valve issue cleared up without pulling head off .. - I'll only try that for "special" otherwise good customers that just don't want to spend a lot on a particular engine.. and much to my surprise, it works VERY well.. CAVEAT - I have not yet used it on a no start due to valves, so I cannot say for certain that it will free up a valve that is stuck so badly that engine wont start.) http://www.blastercorporation.com/Lawn_ ... ne-Up.html