for what it is worth
Electric motors are more torque than rpm, and then they geared the thing down a bit to drive the chain. I would be willing to try some adjustments on the only thing you can fiddle with.
The chain.
Make sure it is sharp, and then lower the gage teeth about 5 thou. Probably means going to 25 instead of 20.... See if that picks up the production a little bit. Listen to the motor if it doesn't sound like it is struggling then you might try another few thou on the chain until you have loaded the motor as much as it can comfortably handle. This can be tricky as a electric motor can handle a severe overload if you don't do it often.
-Pat