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

The engine has a definite knock. While stationary determine which journal is sloppy.  I like to take very thin clear plastic to make up the slop. The kind from blister packaging.  Better would be very thin brass sheet or foil.

I suspect your piston rods are worn. A way to check for that is thick steam oil. Dripping some on it, will improve the running momentarily.

I have a stand alone 365/1 engine just like this… and mine is also sluggish.  Dropping steam oil onto the piston rod DOES in fact make it run better momentarily, thus what you said, worn piston rods.