For both coils to fail at the same time is highly unlikely. Usually, a reduction in power is quickly noticed, but not a total shutdown.
I would study the fuel system closer. Trash in the tank getting sucked into the pickup tube is fairly common. Bugs, dirt and grass clippings get into fuel cans easier than people realize.
A common issue I run across at about this age is the fuel pump pulse line getting cracks in it. When that happens the fuel pump quits working because the line gets hot and swells just enough so the crankcase pulses will not operate the fuel pump.
A spark tester is nice but use only the ones you can adjust the air gap on by hand. Ebay has them for just a few bucks each. Do not get the one with the bulb in them, they are unreliable.
The other item to check is the main power fuse to make sure it is not getting hot or fitting in the fuse holder loose.
The next item to check is under the upper engine cover. Mice love to nest up inside them and grass clipping along with dirt collect and choke down the cooling air fins.
Hope this helps you.