The A3A variant of the engine has a hollow crankshaft, A4A has a solid crankshaft. There are various props that set up a resonance with the hollow crankshaft and cause vibrations at certain RPM, it is quite noticeable as you move the throttle through that range. Check the prop that you are using, not all are affected, there should be a placard in the aircraft.
Most key ignitions cut the right mag. out in the start position but some don't, certainly the older Robins I have flown (like the DR300) didn't. The left mag. is the impulse mag (retarded ignition for start up) so the right one isn't used until the engine has started.
Enjoy the aircraft, MUCH nicer than any of the American spam cans.