Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

1 - Is the atmospheric intake valve opening?  It could be sticky.

2 - It doesn't appear that the exhaust valve is opening much.  A wide gap affects valve timing.

3 - Pull the plug and see if it is wet.  If so, and you have a compressor, blow out the compression chamber and plug to dry them.

4 - Reset the carb needle to 1/2 turn open (I'm guessing for that engine). If no start, adjust carb needle 1/16 to 1/8 of a turn until you get ignition.

It's all about fuel, compression, and spark.  It seems to have compression and for sure there is spark, so the culprit is fuel.