I discovered a way to lighten up the action a bit on a couple of older double pedals that I have, a Pearl Powershifter (the first version) and a Yamaha from the late 80's. Since the left(slave) pedal has quite a bit more mass because of the connecting shaft than the main pedal, I would remove the beater holder on the left pedal, since it's not needed there. Also, I removed the chain cam on the left pedal and drilled out the "webbing " in the area between the hex shaft hole and the felt lined channel where the chain goes. I just use various sized drill bits until the area is mostly clear, then clean it up with a Dremel tool. With the Pearl cam, it ends up looking sort of like the cam on the Tama Speed Cobra, like spokes in a wheel. With the Yamaha, I just drilled three holes about 7/16" diameter, spaced evenly apart. I could probably just drill out the whole area , but haven't gotten around to it yet.

It's not a dramatic difference in either pedal, but it does help even out the feel between the left and right.