912 ULS no more than ~4800 RPM

Did your air intake scat tubing get disconnected?

Hey Bill

After that event, I opened the cowling to see if there something was out of order and I did not find anything obvious. Intake was connected, Air filter was not obstructed.

I suggest to clean the air filter first thing and give it a try . Filters might look good but trust me it might be dirty from inside . It happend to me 3 times in a diffrent aircrafts .

Carlos,

Humidity, temperature and even barometric pressure have an effect on max engine power and will cause a reduction of takeoff RPM.  I routinely see 100 RPM swing in takeoff performance with these changes. 300 RPM does sound like a lot for just a change in weather, but I'm wondering if you had some days of very high humidity or temperature, or both?  Going by the Rotax engine performance chart for the 912 ULS, at 5100 RPM the engine has a max output of about 91 HP, and at 4800 the max HP drops to about 87. So that means the power drop associated with what you are seeing is less than 5% of the engines rated output. It would be interesting to do another static test in different conditions and see what happens. 

Thanks Jeff.

I'll do that in few days. I want to change the sparks plugs and the spark plug caps. 

I have TO in, I would say, more difficult weather and beyond of keeping an eye in the temps everything was ok. I have many hours in a Rotax and I have neve experienced something like this.