Engine will not make power after carb install, post-overhaul

The responses in this thread (including mine) are mostly centered around prop pitch, with Rotax Wizard also suggesting some carburetor setup issues that may affect mixture.  It would be easy to go down the road of a new ground adjustable prop that could be pitched to bring the RPM up.  Still, I’m bothered by the fact that before the carbs were rebuilt and brought back to their stock configuration the engine would spin the prop at 5000 RPM in a static condition and now that’s about 4800 RPM.  Looking at the performance data for this engine, this means the engine was previously making 4-5 HP more at WOT static than it is now.  The carbs were apparently previously modified with some sort of mixture control, but that seems like a big difference for a do-it-yourself carb mod.  Assuming the run conditions before and after were the same ( outside air temperature, density altitude) what could account for this power difference?  

If it were my plane I would double check the throttle lever WOT position, check inside the carbs and if those are okay reset my prop pitch and then see the results.

Don’t overlook Jeff B’s note above regarding ambient conditions. A 200 rpm drop is about 3.5% and is not unusual if ambient (DA) conditions worsen. The engine will spin the prop at x rpm on a cool/standard day but slower than x on a hot/high day. Any chance ambient conditions could be contributing to this issue?

Hi all

Just a comment on Jim's idea.  With a fixed pitch the density of the air affects both the engine and the prop.  You would drop power and thrust. The engine RPM is mostly unaffected since we unload the prop with the lower density air at the same rate as HP loss. 

Cheers

Ahh yes- thank you. Brain cramp! He would have to go to an extreme DA before rpm would begin to fall off. The performance chart stops at 7,500 meters DA so perhaps above that?