Spark problem

[Kmoore]

Having problems with a 18.5 hp Briggs and Stratton motor I have no spark coming out of the coil i disconnect the ground wire still nothing I can crank it over and hold on to the spark plug ends I changed the coil and put a new coil on and still absolutely no spark

 

[Scrubcadet10]

do you know what the correct air gap is?