I've read this entire post. Questions. Have you ever pulled the coil wire and checked for spark hot ? I dont see this question answered. Have you ever squirted fuel in the bowl and tried to start? I dont see that answered either. Have you pulled a plug and tested compression hot? If the valves were sticking open hot this test would confirm lack of compression hot vs cold. The engine only needs a few parameters to run. Compression with correct valve timing. If the valve timing was incorrect it would never run. It needs correctly timed spark. And it needs a burnable air fuel mixture. The only other possible item would be restricted exhaust such as a plugged catalytic converter. Since I'm assuming that it has no converters I would say this is unlikely. Also assuming the engine cranks with reasonable speed hot. That leaves 15 minutes worth of tests above to determine why it wont start hot. After determining if its , spark, fuel/air, or compression. The real diagnosis will begin.
Think simple first.
Doug