Here is the wiring diagram I got off of the web. I wonder if your mag kill wire is grounding somewhere. I would check the wiring on the brake switch or if you can unplug the kill wire going to the mag and see if you get spark. I'd pull the plugs to check the spark because you may not be able to kill it when it starts if that is the issue.
Here is a link to the schematic also.
https://pandpsmallengines.com/pages/...wire-schematic
GT3100 schematic.jpg