I think I know what the problem is. You need this:

Spoiler: Just kidding, of course. What, can't I make a joke once in a while?
Dreadwish is correct: the rotary engine needs the driveshaft attached in order for the rear wheels to be powered.
If you want to use the 13B rotary without the driveshaft, you can replace the transmission script and change it so that it works as RWD without a driveshaft. This should be fairly easy: copy the java from one of the Emer transmissions, rename it appropriately (IN THE JAVA AS WELL AS IN THE FILE NAME), and then change the gear ratios and drive wheels to your liking. I did this myself, and I would post the result for you except that I don't have access to it right now. PM me if you want it, or if you want more help figuring out how to do this.