After installing the MAAM-SIM DC-3 I could not get the engines started. After a while I decided that this couldn't just be due to my ineptitude (which is normally the case), and a quick trawl of the net turned up the following solutions.
For each variant open up the aircraft.cfg file in Notepad.
In the [piston_engine] section change the normalized_starter_torque value to 1.5 (or 2.0), like this:
Changing the power_scalar value to 0.95 or higher also works, but this affects the power output of your engines, giving you an extra 10 or so knots at 2000rpm which could mess up your flight planning.
Some people have also found that lowering the FSX target frame rate to below 30 fixes this, but this didn't work for me.
I got all this information from this thread on Buffalo Airways.