Can't get it started

Compression, spark, fuel. That is it

Compression. Has to be "enough." If the engine is severely worn, valves burned or CAM DRIVE SLIPPED it may not have enough compression and of course cam out of time never good

SPARK. Needs to have a good hot spark. This is why I start by checking spark right at the coil with a grounded probe or gap. This shows you what you have. Nice blue spark at least 3/8" long. Of course the spark has to be IN TIME. Since you mentioned timing light, you can check timing "on the starter"

Obviously check plugs, coil wire, condition of cap and rotor.

FUEL. FRESH fuel. And make sure it's actually gasoline. About 1/2 to one teaspoon in each carb throat SHOULD result in a nice healthy "second or two" blast of "running" from the engine, even if the carb is plugged, etc or not getting fuel.