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

If the pump is connected try running it with it disconnected as it may be causing to much friction
I would use the disconnected pump to manually to fill the water jacket first.
Another simpler problem maybe to much dead space. I would remove the hot cap and measure the distance from the bottom of the displacer to the engines bed plate and check the depth of the hot cap you only going to need a couple of mill space
The engines ratio should be around1.5:1