Worn Air lifts will cause this predominantly. They also will throw slight clumps if you cut early in the morning before the dew has dried off. The air lift acts like a fan in a vacuum, lifting the grass up while also carrying it over to the next blade to be blown out from under the deck.
Tire...
Kohler and Kawasaki's oil are made by the same manufacturer.
I learned that at one of the engine service schools.
They also contain zinc, which can poison a gas engine's catalytic converter.
They are all I use in small engine repairs at my shop so those two are all I will use.
I also repair...