These engines draw some amps. Any imperfections show up. I suspect that running in conventional, may cause the amp draw to be higher so the sparking is more severe. Having the rollers cross over switches and joints makes the problem visible.
I just got a new Bigboy. I had to turn the handle on a Z4000 all the way up to lesson the draw on the rails.
I do know from experience, that motors run better and cooler in command mode. They draw less and can do more. On my outside G scale layout, I have the voltage turned up higher to run big trains easier. When 4 to 6 engines in consist are on a mainline, the amp draw is surprising low that way. The grades outside are bigger. The cars are much heavier. Yet I see higher amp draws inside with O scale.
