Check out the rotax-owner.com site. On there, the consensus seems to be to use Gates Barricade carburetor lines. Fuel injection lines are too stiff.
I thought sure I had added some lines on my 912ULS on my gyro but I don't see where I did. My lines are Gates 3225 7mm from the factory (in Italy). Trying to get properly sized barbs to install my fuel flow was a challenge: I ended up using a 5/16" hose barb because 1/4" was too small, even though 7mm (0.2755") is closer to 1/4" (0.25") than to 5/16" (0.3125"). In any case, it may be best to try a small piece of 1/4" and 5/16" to see which fits yours best, then buy that in Gates Barricade. But I'm pretty sure it'll end up being the 5/16".
Hope that helps.