That is Bad advice. They would not tell you that if they had extensive Rotax 9-series tech support & accident investigation experience
In my opinion, if we could go back in time, the airbox should have been mandatory for the 100hp. A few OEM's would have been very unhappy, at first, but it would prevent so many problems.
Airbox advantages:
Carbs cant get pitched off (see below for contributing factors)
Better starting characteristics, prevent sprag failure by stabilizing the carbs. shaking carbs in many aircraft with weak mounts, such as many amphibs, have caused much grief.
Ideal connection for float bowl vent. this is very important.
Vent tube inside airbox is perforated so that any fuel in airbox is drained but the vent line is not exposed to vacuum/pressure (from slipstream or wherever the drain hose is routed)
Less strain on the carbs sockets: You do not have to perform SB-912-030 "carb socket inspection" with a airbox properly mounted.
Drip trays built in.
Carb heat
Help equalize and smoothes out airflow
More efficient: less CO and maybe a little more power.
