As was said I would think if it had spark and gas it would "pop" regardless of all other issues. But... not always. If you can see spark, even weak spark, generally my thoughts go to gas. Are the plugs wet after cranking? Have you confirmed gas actually getting to carb? You have as many as 3 screen filters and a fuel shut off. Does it pour out of the fuel inlet when disconnected? Is the bowl full? Is the ignition switch on when you are cranking... not just testing? Ha... i've done that before.
And did it run before or did you change all those things and now it won't run.