This is a Tecumseh 6 hp big block horizontal engine with 3/4 inch shaft , keyed and tapped for a bolt. These engines are good for mini bikes or go carts. This engine has great spark and good compression and a good working pull starter. Comes with a new carburetor. Model number 143-566002 Serial number 5266. I searched up the serial number and is shown to be a 6hp engine. Email me with any questions.