Engine Starting

The Rotax 912 owner's manual says:

Activate starter for max 10 sec only (without interruption), followed by a cooling period of 2 minutes!

Really you should try to find out why your engine does not start easily. I would suspect the battery, starter, solenoid and cable connections. You could charge the battery for 30 mintues before trying to start and see if that helps.

Assuming the starter rotates the engine at a normal speed, a few things come to mind for a hard starting engine. First is  technique.    On a Rotax, the throttle should be fully closed when using the choke.  Also it may be worth double checking the spark plug gap, and visually checking that the choke and throttle cables have proper range of motion at the carb

Preheat will help.

Definitely check to make sure your starting carburetors (choke) are being fully activated by the cables.

I use a closer spark plug gap during the cold months, seems to help