John,
The problem with these locos is a combination of small cylinder
diameter, light locos and throttle needles that are too blunt.
The only one you can control easily is the weight -- put some weights
on the loco in inconspicuous places, or always run with a train.
The next easiest is the throttle. What you want is to put a sharper
point on it, so a turn of the throttle handle won't change the opening of
the steam passage as much.
If you have a lathe or a drill press, remove the needle by turning the
handle counterclockwise several turns. Then, pull the needle out of
the throttle body. Remove the handle and O-ring and chuck the
needle into your lathe or drill press. Get a sharp (NEW!) file, arrange
a steady rest for it, and hold both ends of it with both hands. With the
needle spinning in the chuck, carefully touch the file to the tip and
work the point into a somewhat sharper shape. When it's shaped,
squeeze some 400- or 600-grit sandpaper on the tip, followed by steel
wool to polish the surface.
This has helped me on a Mamod and a Ruby, and it's a tried and true
old remedy for runaway steamers.
regards,
-vance-
Vance Bass
Albuquerque, New Mexico, USA
Small-scale live steam resources: http://www.nmia.com/~vrbass
