I have recently bought a secondhand Bachmann motorised tamper, and I have found a strange problem. The motor seems to run ok at slow speed, but as soon as I try to go up to a slightly higher speed, the engine just grinds to a halt, and the motor simply spins. I am not sure if it is a gearing problem, or a lack of ballast weight. Has anyone else had a similar issue? All and any advice gratefully received.