When you changed the plugs did you notice the condition of each plug?
Looking to see if the misfire is dedicated to one or the other cylinder.
If the fire was even on each of the plugs I would keep looking at the fuel side if the engine, perhaps a fuel pump, gas tank vent , gas cap gaskit, maybe drain the tank.
If the plugs vary in carbon we will look to the electrical system, wires ,coil, ignition wires, rev limiter. Hope you locate the problem with these ideas.
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