Make sure the axles are free of debris and lubed. A number of years ago a co-worker gave me a box of old Lionel engines to see if I could get them working. All had carpet lint and animal hair wrapped around the axles. Once cleaned and lubed they ran fine.
My Williams brass N&W 4-8-4 J weighs over 14lbs and seems like each passenger car was around 2lbs each. Of course the J has a big honkin motor but it stays cool.
I tried running engines w/o traction tires and found they didn’t do so well so I found suitable replacements and put them on. I’ve found using small bladed screwdrivers in each hand I can work them around the wheel until they’re on. One engines wheels were narrower than the tire, all I did was run the engine upside down while holding an exacto knife to trim the width of the tire so they would fit in the groove.
