Kawasaki Engine Fouling Spark Plugs

Bought a used scag 61 in. from my nephew last summer. It is a low time machine with 421 hrs on it. Right off it was blowing black soot, that is after I serviced it according to the manual. Engine is kawasaki model FD791D. I don't know anything about fuel injected engines but I got through the summer last year by changing and cleaning plugs every 30 or 40 minutes. Is there a diagnostic reader for this like cars ? I will say I love the thing...from craftsman lawn tractor 3 days a week to turf tiger 1 day a week! I mow about 4 acres .
Spark plugs get covered with dry soot. Anyone know any common ailments this engine is known for ? Don

Re: fouling plugs

Yes there is a reader
You can diagnose without one
Get the kawasaki manual from here https://www.mymowerparts.com/pdf/Kawasaki-Service-and-Repair-Manuals/