pault36

hi all i've got a bedford mk sat on the shopfloor that has a b81 petrol (stolly)engine bolted to the back end. this drives a winch which is used by the local gliding club to tow their gliders into the air. i'm after any tech info on the b81 as i'm servicing it as a favour in particular anyone know the plug gap as its running pretty rough at the mo and all the plugs are covered in soot and it stinks of unburnt fuel any help setting up the solex carb would be greatly appreciated too. thanks