This series of engines are usually to be found on ride-on lawnmowers and garden tractors.
They have the two cylinders opposite each other in line, with the spark plugs fitted fairly centrally on each side of the engine.
The air filter is an oval cartridge type filter inside a metal cannister at the front of the engine. The carburettor is below the air filter cannister and mounted on cast manifold that runs across the front of the engine. The fuel pump is fitted directly to the front of the carburettor.
The Model, Type and Code numbers are stamped either into the pressed steel cowling just above one of the spark plugs or on a small alluminium plate rivited to the top of the cowling. The Model begins with either 40 or 42