Hello all, after a shamefully long period of quietly keeping up with all the messages on this great forum the time has finally come to formally introduce myself (the reason being that i have a problem with the aircraft of course).

My name is Jan, i am a 29 years old aircraft engineer in the Netherlands and recently I had the chance to purchase a Kitfox 4 speedster.
The aircraft is a great flyer, pretty basic equipped thus light. It is something of a flying project however.

A problem did arise with the airplane. On a flight a couple of weeks back I noticed that when pulling the carb heat (exhaust heater type) the rpm of the Rotax 912ul increases instead of decreasing, what you would expect.
The difference in engine power is quite notable. During full power cruise the rpm rises from 5500 to slightly above 5800, and the max. speed increases from 90 mph to around 98 (the airplane does not have any fairing or other fancy streamlining stuff).

First I checked the airfilter, no problem there.
Then I pulled the carbs apart. I did find the little dampener o-rings on top of the needles where not installed. The needles where pretty worn out so I changed those, as well the needle jets and the float valves and brackets.
The needles where installed in the #3 position.
After adjustment and synchronisation I did a little test flight....no difference.

To me it seems there is something wrong with the mixture, but I cannot figure out what anymore.

Any help would be greatly appreciated!