My Scagg lawnmower was having a very ruff idle and getting worse. I purchased a new carburetor and replaced it. I had to do a couple small modifications to get it to fit. When I was done it ran great with no further adjustments.
The carburetor is listed on Amazon as
ALLCARB Carburetor 150047060 150037100 Replace for Kawasaki FH580V 19Hp Engine Exmark Replacement for John Deere 235 Mower
for other maintenance I have done on this lawnmower check out the rest of my channel