See the FAQ under "Swamp proofing" Short story, if the vent is submerged and the engine stalls, you run the risk of pulling water into the case when attempting a restart. Same for the carb lines, but you don't need to stall. If all four lines are submerged, it will draw water into the bowl. My '05 WR has the vent lines split for about an inch plus an angle cut. I still ran the two top lines into the airbox.