The Rotax VMF is a water cooled reed valve direct drive 100cc kart engine (ICA) from Rotax that was introduced in 1999. It was the last Rotax 100cc direct drive reed valve engine. Since then, Rotax have shifted focus towards the Rotax FR125 Max TaG engine and discontinued their 100cc line.
The Rotax VMF is roughly the crankcase of a Rotax VMD or Rotax VME with a water cooled cylinder and head on top. There are earlier Rotax 100cc water cooled engines (+/- 1995, type designation unknown), but those are identical to the Hezemans Rotax 100cc Reed Water Cooled, only with a Rotax logo instead of a Hezemans one on the side of the barrel. The VM/F has a distinctly different cylinder and head shape. These engines use a right hand side ignition and a closed crankcase half on the left. This construction uses an engine sprocket that is locked against the ignition rotor. These sprockets are difficult to source, but can possibly be machined from standard sprockets.