My only complaint (and pretty much everyone's who does slow-speed switching with MTH engines) is the little lurch these engines give when starting but at 3-4smph they settle down. I'll live with it compared to the rocket-starts of most O Gauge engines. The exception is the Atlas SW8/9s which start beautifully
Lew, this issue annoys me too, and here's my take on it... MTH, K-Line, Williams all use two vertical motors, but unlike postwar Lionel the worm gears in each truck are self-locking. Thus one motor truck cannot "push" or help the other. My testing without speed control showed that neither motor is really happy below 800 RPM (about 10 mph.) The speed control will force them to run at speeds below that, but reluctantly. And not always both motors at the same time. If one motor starts to stall you'll see bucking, "chuggle," or a lurchy start.
Most of these locos are grossly overpowered. A single motored loco with die-cast trucks and rubber tires can probably pull 15-20 freight cars. So if you really want the smoothest possible starts, one reversible mod anyone can do is a radical motor-ectomy! Remove the motor without the speed control sensor and tape off the wires. No, the loco won't pull 40 cars anymore. But it *might* start and run consistently at 2-3 mph instead of 4 mph or more. Because now the motor with the sensor won't have to fight against its twin in the face of transient frictional events. Lionel's LionChief NW2s have only a single motor. They run smoothly and still have plenty of pulling power.
Over the years, MTH changed their catalog text related to PS2. The early catalogs touted smooth operation at 3 smph. In some later catalogs the claim was increased to "5 scale mph or less," possibly to reduce warranty complaints of poor starting and jerky operation at the slowest speeds.
Lionel beat the lurch by switching to back-drivable gears in their dual-motored Legacy locos. The two 5-pole motors in those trucks can actually help each other, delivering as many as 38 power pulses per inch! Going to a single motor with a very low gear ratio (like the Vision Genset) would be another definitive way to get smooth starts and reliable single-digit speeds.
