912 having low power at takeoff

[Wheels]

My Kitfox IV has a 912UL.y I usually get 5800 or close to it at take off with my 3 bladed Warp Drive. A Mechanic in the hangar said he thought the engine sounded rough and offered to sync the carbs. They were out of sync. now are smoother but I cant get more than 4900 RPM at max power for takeoff. He said the throttle stops are set right so that the butterflys are full open at full throttle but I am not able to produce more than 5100 static RPM and the 4900 RPM at take off only gets me 5100 when I level off.
He checked the needles and said they were set to specs. The diaphrams are new. Any Ideas?

[catz631]

You should be getting at least roughly 5200 static (WOT) at the beginning of your take off roll. This is per a recent Rotax service bulletin (so as not to overload the engine case..ie: cause cracks)
Full throttle in flight would give you some where around 5600rpm.
These are the figures I was getting when I had the Warp taper tip on my 912UL (I am now using a smoother ,lighter, Kiev)
If the butterflies in the carbs are wide open at full throttle then the only thing that I might suggest is to change the prop pich to achieve the proper rpm .
Dick Maddux
Fox 4
Milton,Fl

[Monocock]

I'm no expert but I do agree with Dick (who knows more than me about these things).

5200 is the ideal static to give a good combination of climb and cruise through the range. If everything is ok within the engine and it sounds smooth throughout the power range, re-pitch for 5200 static and see how you go.

It just seems a little weird that after a carb sync that you are 900 rpm down on what you were before with the static.

[HighWing]

Carb synching is done by minute adjustments of the throttle cables. In the original set-up or if installing new cables I can see the need to check for overall carburetor function, but when I did a routine sync - assuming the engine was running well - it was just very minor adjustment of one throttle cable. Sorry to suggest this, but in my mind, if the engine was running well and then "X" was done and the engine is no longer running well, I can't help suspecting "X". My first priority would be to verify that the carburetors are set up correctly. If they are, then the mystery deepens.

[Wheels]

The mechanic and I are new to Rotax so we are in a learning curve. I called a mechanic who regularly works on the 912 and owns one. He is coming to save us. I'll post the results.

[cap01]

wheels ,the 912 is a little different animal . once you learn the quirks they run good . if you have the belcrank throttle system , get one of highwing llcs throttle links . makes syncing carbs a snap , well worth the 50 bucks

[catz631]

Amen on the "throttle link" !!! It's GREAT !!!
Dick

[Wheels]

Fixed the problem, yes it was out of sync carbs and now it is fine. the tach is reading a little low as well which made the problem seem worse than it was. the plane is flying at VNE straight and level at 5200 RPM.

[DBVZ]

Hijack:

Has anyone done this piston change for more power with the 912UL, and can report on difficulty, performance change, satisfaction with the conversion, fuel you use, changes in CHT and EGT and other temps? It says 92-93, or 100LL; so I am expecting most will use 100LL as the easiest to get and most effective at the higher compression:

http://www.craftworks.biz/pistonsite/912sales.htm