ROTAX 912 Leaking Carbs

1.Float Needle valve inspection artical 3.3.10 see attached.

2.Floats bracket adjustment's 0.5 mm for 912.

3. Float needle valve leakage Test  artical 3.2.2 chapter 73-00-00

Hope you do it.

Now I don’t really like showing my ignorance but today is an exception.  How does the electric pump cause the problem if it is turned off?

It doesn't cause the problem; turning it on when the engine is not running just helps to diagnose the cause.

Switch engine off when running rough and spilling fuel, turn off fuel tap, check fuel level in bowls should be 1/2” down from bowl edge. Do same test shut off engine when running smoothly no leakage, note the difference.

sometimes it’s just rough running shaking carbs, rebalance carbs.

Weigh floats when they are dry. 2.78grams  is perfect for older series floats, latest floats are closer to 3.2grams each. Require adjustment of float arm. 

Hi Riley,

3 things that most likely are causing fuel to come out the vent tube.This just means the fuel level in the carb is too high and coming out your vent tube. #1 & #2 are the usual suspects and are easy to rectify. 

1. heavy floats

2. Brass float armature out of adjustment. This should be 10.5mm  from the edge of the carb bowl edge to the top of the brass armature. This must be checked with the carb upsidedown. 

3. Needle valve not seating properly. Could be debris or even a bad needle valve. This one's last on my list.