Hi! I dug out my train set from the early 1980's, everything's great except the engine. When the power is on, it wants to run like normal when either the back set or the front set of wheels are in contact with the track, but not when both are connected. It worked fine all those years ago, and was so much fun to play with. If anyone has experienced this symptom and knows how to fix it I'd be very grateful. Thanks!