My son has this locomotive and it only appears to smoke when the engine is in reverse.
The engine is about 5 yrs old.
Any thoughts?
There is likely nothing wrong with your locomotive the smoke is more of a novelty effect and is not one bit realistic, however I realize there are those that opt to use the smoke machine every once in while for whatever reason. The unfortunate thing is that there is not anything you can do to fix the problem. It would cost you $25 to send the loco in just to get another loco where the smoke will only work off and on. As long as the locomotive runs okay, I would not send it in, it would not really accomplish anything.
OR
You could choose to try a new smoke unit.
http://estore.bachmanntrains.com/index.php?main_page=product_info&cPath=66_68_155&products_id=1706