I'm not that familiar with this machine, but I'll throw these out there in the event they are relevant to your machine.
1. Did you check the spark plug wires by measuring the resistance in each one (ohms)? Also check to make certain the wire insulation is sound and not shorting along it's path. Sometimes it helps to test this at night, so the sparks are easier to see.
2. Did you do a compression check? Report finding if so.
3. Did you check float level to make certain it isn't too high, float sticking, saturated with fuel, etc? Could also have a leaking needle/seat.
4. Did you actually take the carb apart and verify all passages are clear/clean without obstructions?
Do you have a spark tester or a timing light? I've used both to see if the miss is fuel or electrical related. The strobe action of the light will be obvious when there is no spark.
2012 JD855D OPS Black Poly Roof, Deluxe Cargo Box, Front and Rear Protection, Power Lift, Front Hood Rack, Rear Screen (homemade), 800 Watt Inverter, 2500lb Winch installed in cargo bed, Front and Rear LED auxiliary lighting (4" square 27 watt), Front and Rear CV Guards, Koplin Side Mirrors