As for Dewights question yes it does want to move a little with the throttle closed and the johnson bar ingaged.
Just for clarification, you do have the johnson bar centered (ie, off) when you're trying to blow down the oiler, and the throttle valve open, right? When you run out of gas, center the johnson bar and close the throttle, otherwise the steam will bleed out the valve to the cylinders. Open the oiler drain, then open the throttle to blow down the oiler (keeping the j-bar centred)