My Kawasaki FS481v starts perfect (half pull) seems just fine when I first start. After it starts to get warm it starts to sputter and has a little backfiring. I've noticed that when the blades are engaged and I'm mowing it doesn't do this. If I just have it in transport mode or just sitting there it starts to sputter/backfiring. I've replaced the spare plugs, hooked up a spark tester and that shows nothing wrong (ignition coil). I did think one of the ignition coils was bad as when I was testing it I had the mower on, I removed the right spark plug connection and the engine RPM dropped and had a little sputter. When I did the same process on the LEFT side there was no drop in RPM so I assumed that ignition coil was bad. I thought I would test it first before spending the $50 for the part so I got that inline spark tester and the "light" showed the same thing for both. I don't think the issue is the fuel filter as I would think it would run weird all the time with that. The mower is only 2 years and I'm the second owner so I'm not sure about any other adjustments the previous owner made. Value adjustment time? I honestly have no clue, but could use some help on this one as I don't feel like taking it in. It still runs really STRONG outside of this.