The speed varies when moving

[Ron Zee]

I recently got a used F-9 diesel loco and it seems that at about 50% power, it'll go fine but if I speed it up it'll go faster few about 15 seconds then it'll slow down a little then a few seconds later, it'll speed up again. Rinse and repeat. What the heck would cause this? I've changed out the trandformer, speed control and did the best I could cleaning the engine. Is it wearing out? Thanks for any help.

[Ken G Price]

If you have not cleaned the wheels and track you should do so.
If it has not been used for a long time then It may need a good cleaning to remove any old lubricant, dirt. hair, etc. It may also have hair and lint in the wheel gear tower and around the axles
It could also be that the track is not making good contact between section.

Does other engines do this?

[Ron Zee]

No, only this one. The set came with a 0-6-0 switcher that runs fine, (except uphill) and I have a 4-8-4  class J Spectrum that runs fine on the track too.

[bobwrgt]

The trucks and wheels pickup power from the track. They must be clean. On each side of the truck is a copper strip that transfers the power to the frame. If it has been sitting for awhile these can also get dirty and corroded. clean the area of the frame where the strip hits and clean the edge of the strip. Should help.
Be sure track is clean.

Bob

[Ron Zee]

Guess I need to try dissasembling it and get to cleaning. I'll let you all know.

[James in FL]

Remove the shell and clean as Ken and Bob suggest and while you have the shell off, clean the armature as well.
My weapon of choice is CRC® QD Contact Cleaner No. 02130

Good Luck