KZ750B ran 3 days ago, now backfire no start, helllp

I have a 1979 Kawasaki. Kz750 B4. I stopped riding it 3 days ago. And then it won't start. It backfires feels like it's flooding. Ran like a champ 3 days ago, now wont start. Pulled the plugs smelled like gas, cleaned them they were fouled a lil. Made sure the coil was connected saw spark. I could use some help as an under the tree mechanic I learn by experience

I'd do a tune up. Valve adjustment, point gap and timing. You do have a factory maintenance manual, right? Metric tools? Carb rebuilds might not be out of order either.

Pull off the engine oil filler cap and sniff the crankcase. If it smells like gasoline, the fuel petcock and at least one of the carburetor float valves have failed. This will allow fuel to trickle into one or more cylinders and then run past the rings into the crankcase. If this happened, the petcock will need rebuilding and the engine oil and filter need to be changed. It would also be a good idea to clean and polish the float valves and seats.