It is on a cub cadet LTX1040. 19.0 HP Starts fine then surges and backfires. Removed carb and placed it in ultrasonic cleaneer through four cycles then blew it out with air. Still doing the same thing. If I hold choke closed some, it will flatten out. Suggestions please before I buy a new carb. Also drained gas and filed with fresh,

Hello, I have an older Scag SSZ 61" zero turn mower with a Kohler CV22S twin engine that won't start. It cranks fine but appears to have no spark. It will not fire at all, even when using starter fluid. I did have trouble starting it occasionally last year, but assumed it was a bad battery. I just replaced the battery today as part of my diagnosis. Upon trying to start it, it cranked slowly so I tried jumping it with my car. It tried to start, stumbled a few times and then quit. I continued to try starting it with no stumble or firng at all. I pulled the engine cover and found a mouse nest and a lot of droppings along the RH side of the engine (facing the carb from the rear of the mower). I cleaned that all up and inspected the wiring and found no obvious damage. Put the cover back on and found the same result. This was last weekend. I replaced the battery since it was bad. No change. It seems to have the SAM system in it. One odd thing is that it also has a jumper wire from one of the mounting screws of the rectifier-regulator to one of the mounting bolts for the engine cover. I'm assuming it's a ground, although it must be grounding through the screw as the cover is plastic. That doesn't seem right and no housing ground is shown on the wiring diagram. I'm going to go through the manual trouble shooting, although electrical issues are something I'm not familiar with. Any tips would be appreciated. Thanks,