Would definately agree with Vince as the mounting pad along side the venturi is most likely for a manual choke making a strong argument that this is off an older four stroke and do note that hole in the side of the venturi with the adjustable screw blocking definately makes this a bleeder carb which makes a strong case for many older four strokes.

Nope have no clues as to what its off of but heck everyone loves a mystery

John