When your locomotive has been properly railed,
slowly advance the throttle until the locomotive begins to move. This may not happen until the throttle reaches 30 percent or more. All locomotives respond differently, and different power supplies behave differently as well.
When the locomotive is creeping along the track at the slowest speed you can achieve without it sputtering and hesitating, make a note of the throttle setting. This is your minimum throttle for this locomotive; you don't want to set the throttle below this value unless you turn it off completely. The top photo shows the throttle at 30 percent.
Next, increase the throttle setting
slowly until you feel that the locomotive is going as fast as it can
safely. This is your locomotive's maximum throttle setting; make a note of it. This is an important number to remember!
Some locomotives have motors so powerful they will jump the track if you enter a turn too fast. The last thing you want to see is your beautiful new locomotive flying off of the table and crashing to the floor. And an O scale locomotive is so heavy that it could break someone's toes if they were standing in the wrong place. The bottom photo shows the throttle at 80 percent.
I have a Lionel
Atlantic class steam locomotive that was made in the 1990s. When used with a newer Lionel CW-80 transformer, its minimum throttle is 30 percent, and it will jump the track at 55 percent. Of course, this means that the locomotive has plenty of power for pulling very long trains. But I have to be very careful to watch my throttle settings when running this locomotive.