According to my research on this forum's history fuel leaking out the 912 carb vent tubes around the idle rpm is quite common. Mine was doing this a lot and installing a new carb overhaul kit (level 3 service pack) helped but didn't eliminate it completely. The floats were visibly floating and not sinking and they were below the spec dry max weight of 7 grams a set. My engine was getting hard to start as well. Then someone on the Rotax forum suggested I lower the float levels by bending the tabs on the float valve armatures. The idea was to reset the float levels to get the fuel level in each bowl at around half full at idle. Each time I had previously pulled my float bowls off after the vents were seen leaking the bowls were always full to overflowing. So I bent the little tab on the float armature accordingly and lowered the fuel level in each bowl. After that, no more leaking out the vents and the engine starts right away and idles smoothly down to about 1800 rpm. Below that rpm the left carb still vents a little gas occasionally so I probably need to lower the float level in that carb just a little more. Bottom line for me seems to be that the fuel float level was originally adjusted too high and adjusting it down appears to have solved my hard starting, rough idling and fuel venting problems. I suppose there is a fuel float level setting that is too low and may cause other unforeseen problems, but for me the setting that equates to a fuel bowl level around half full appears to have solved all my rough idle operating and starting issues. The engine seems to run smoother overall and I haven't even done the pneumatic carb sync yet. At the moment I'm a happy camper.