Here is a good video of how to install and how the soft start module works.
http://rotax-owner.com/index.php?It...iew&id=49:ssm&option=com_content&view=article
The "kickback" is something you want to avoid at all cost. You will know it when it happens. The prop stops for 1/2 a second, (taking up the back last in the gear box) and may even come to a complete stop as the prop drags the momentum of the engine down to the point where the engine (26 degrees BTDC) fires and causes the engine to "kick back". This is EXTREMELY hard on the $1,000+ spag clutch, so stop the starter if you get into this and figure out what is wrong. Typically, you need to preheat the engine more if you have not had problems before and now it is cold.
Here is a video of what a bad sprag clutch looks like. Notice how the prop stops for just a split second, and how the operator thinks by keep ing the starter going it will somehow magically fix itself. If you get a kick back stop. Try something different.
http://www.youtube.com/watch?v=ga5AgzkPNgM
3 days and $1,000+ to repair yourself, or $2,000+ if you hire someone. You have to pull the engine, and have a very specialized gear puller that costs $200. There is a reason the soft start module is standard equipment now. IMHO better get one and put it on.
Other causes of the sprag clutch going bad is constant 100LL use. Rotax says to just decrease the oil change intervals to 25 hours, but IMHO 100LL should be avoided for daily use. If you are going cross country fine, but use mogas when ever possible. Even occasional use of 89 octane mixed with 100LL is better than straight 100LL.
Hopefully, I don't sound like a know it all, certainly I am not. Just trying to get info out to RV-12 owners. I have owned several Rotax 912 (80 & 100HP) and have delt with these issues for more than a decade, and I learned the hard way on replacing the sprag clutch. It is MUCH easier to avoid the problem now than to fix it later.