engine won't start

That big belch could have caused it to jump timing. But you would usually sense the engine turning over much quicker. What does that mean when you say "It seems to be firing OK"? If it were firing OK it would be running. If it's flooding maybe you only have a choke problem, which could have contributed to the belch. Hold that choke wide open with a screwdriver or have someone assist you in doing so. Holding the gas pedal to the flood as you start should unload the choke as well. If this works than you could have a bad choke pull-off, which was very common. That's a small vacuum valve the pulls the choke open when the engine starts. Usually the diaphram leaks and fails to hold vacuum. Epoxy around the crimp edge of the valve will fix the leak unless the diaphram is ruptured.