Small Engines (Lawn Mowers, etc.): simplicity lawnmower repair, cables and wiring, sore thumb

Question
i found a 1966 simplicity wonderboy 401 (model number 990357) riding lawnmower and rebuilt it but every time i get it to start the engine revs and doesnt stay at a constant speed.  what might be causing this? also i have not been able to find a manual with how the cables and wiring is supposed to go so if you might know where to find one let me know.  Thanks very much for your time.  Jacob Clark USMC  

Answer
JACOB, IT SOUNDS AS THOUGH THE GOVENOR IS NOT HOOKED UP.
IT IS USED TO SMOOTH OUT THE ENGINE'S RPMS.  IT IS OPERATED
BY THE COOLING WIND CREATED BY THE FLYWHEEL.  I LIKE YOU HAVE NO MANUAL AND THIS ADVICE IS STRAIGHT FROM THE HIP.
TAKE A LOOK MAYBE IT WILL BE STICKING OUT LIKE A SORE THUMB.

GOOD LUCK, AND KEEP YOUR HEAD DOWN.
GEORGE