My Bolens 160hydro Suburban Tractor 'Eliminator' has a 16hp B&S Model 402707 engine. I need to know the Air Gap measurement between the coil and the center rotating fins thingy, that supplies spark to the spark plugs. I have been told that the gap should be 10thou and someone else said 20thou. Surely there must be a correct measurement for optimum performance. Can anyone please,please tell me what it should be?????? The grass keeps growing!!