Without knowing what engine or what kind of mower it is this is just a guess.
But, it is possible that your flywheel and/or coil have gotten rusty and are not getting the conact that they need to make the spark. Try removing the cover and sanding the flywheel and coil.
If it is a riding mower with a key switch there are many possibilities including anything from a bad switch to one of the safety switches.
0.030 is the gap for briggs and stratton 4.5 hp mower
.030
.30 thousands
What is the gap on the spark plug on a Brigg's stratton lawn mower Model#31P777 Type 0348E1?
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30/1000's
official site for Briggs and Stratton Spark Plugs is: http://www.briggsandstratton.com/maint_repair/routine_maintenance/choosing_spark_plugs/ The proper spark plug will depend on the type of 6.5 HP motor that you have. Briggs and Stratton made several different ones and the best way to get the proper plug will be to call an authorized Briggs and Stratton repair shop with the mower make and model numbers.
not getting fire 4.75 briggs statton lawn mower
A Champion CJ8Y or J19LM will perform fine
.32
You can set most plugs at .030 and be safe.
Brigg's and stratton 5.5 hp on the craftsman push mower your gap tool set the gap at .025-030 for briggs 5 hp