912ULS carb overflowing

yes, an early model. Has seen around 20 years of service by now.

A few other things to consider. Have the carbs been synced? Has the prop been dynamically balanced? Strong vibrations can keep the float needles from sealing.

Hi Charlie M

When you say "spilled" I take it you mean fuel has been ejected out of the breather tube?

I had this problem with my new 912ULS - after much debate on this Forum, that did little to improve the problem,  I found a 10 year old reference from Roger L.Seems that having anything that interferes/restricts the carburettor rubber manifolds ability to absorb/dampen vibration will cause the float bowls to overflow.

In my case it was the way the custom airbox was attached to the carburettors - check this out as a possible cause.😈

Yes, carbs have been synched.

Dynamic prop balancing is on our to do list, since that had been suggested to us as well.

Remark though: We had props dynamically balanced before and you could tell a before/after difference. However here, the engine actually already feels very smooth. So while we still will do it, we don't think this is the root cause.

correct. it spills out the breather tube. In large quantities.

Nothing besides the intake air-hose attached to the carbs that would restrict how it moves. Same setup also ran just fine on old engine.