This is an engine I am very familiar with - Generac GN570.
It was actually made by Briggs and Stratton.
The issue I am having is that I need to identify the generator itself.
What is the serial number of the generator?
Are there any markings on the front of the generator, such as Q55, NP60 etc?
We can do a couple of things, though.
Remove the shroud over the top of the engine.
You will see 2 coils - one above each cylinder.
There is a single black wire coming from each coil (not counting the spark plug wires).
Unplug both of these black wires, and check for spark again. Check both cylinders.
Do you have spark with these wires disconnected?