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

I believe the key to getting a much slower running speed would require the lighter springs along with making heavier flywheels. Remaking the outer steel “Rings” on the flywheels maybe .100 larger or .100 wider or both would add significantly to the rotating mass. It needs more rotating mass to be able to coast slower between firings.
You could machine a flywheel ring that just fits onto the original as an experiment and attach using super glue. If it works great if not enough weight then heat the glue some to remove the rings.