Kohler engine.
Could be fuel issue, water in fuel, restricted line in the tank. Or because it IS a Kohler, I wouldn't be surprised if an ignition coil or both have failed. In 30 years working on lawn mowers, I never ever once replaced a Kawasaki ignition coil, one or two briggs, and hundreds of Kohler's. They have a kit for the SV series to replace the DSAI coils with a newer style that usually lasts. I do not know if they have them for the CV series that is on the ZG20/23. Check with Kubota dealer. If the part number supercedes to one that is considerably more expensive, it's probably updated to the new style.