A Kart has 4 letters and starts with the letter K. A kart has wheels and can be manually pushed or powered by an engine.
Keeping. Knuckle. Keyhole. Keynote. Kindred. Kingdom. Kitchen. Knavery. Knavish. Kneecap. Knocker.
Kenspeckle, for one.
kangaroos
Kicka$$.
understand
applesauce
UndertakerUnderwear
abbreviate
astronauts
adamantine, allegories, arithmetic
department
satisfying
originator
Gastronomy
extinguish
Toothbrush