Loss Of Power at full throttle

Might have some debris in that carb. 

UPDATE: 

Just an FYI, I am working with a rotax certified A&P on this. 

New air filters are in 

Carbs were resynced again (they were off a hair)

Fuel filter clean no debris

Plugs looked great, burn looked fine, cleaned and re-installed to proper torque setting

Test flew and issue still present.

Test flight: Runup was fine, a little under 100 drop from each mag. Took off, full power, about 5100 RPM, made my crosswind turn, made a turn onto downwind, was on downwind at 1k AGL and the engine dropped power all the way to 3500rpm from 5100rpm. Engine lost power, backed off the throttle half way and it was humming fine at 3500rpm, whereas full throttle at 3500rpm was stumbling. 

Landed fine and pulled the carbs, some lead debris in the bottom. Floats weighed out good. Got a full carb overhaul kit to be installed. 

Next steps if the carb rebuild doesn't fix it? Both mechanical and electric Fuel pumps aren't very old. 

Rory. I’m having almost identical problems. I’m in Phoenix. Would love to know what you find when you resolve yours. Please email me b737franc@gmail.com. 

Only happens in flight, and not on the ground? If so, how are your carb float bowl vent lines routed?

 Hey All,

Yes! Jim, that's exactly what we found. We couldn't see it while on the engine, but when we removed one of the carbs there was a huge hole in the carb static vent line and the gentlemen (previous owner) who replaced the filters before me, also had the tube facing into the airstream. So once I leveled out in flight, guessing that tube then got positive pressure, thus causing the issue. As I recalled the last two flights, I remembered the issue occurred only once I leveled out the airplane. Hoping that was it.

We did, however, do a full overhaul on the carbs and found the float bowls full of hard lead sediment. Upon disassembly, We didn't find any busted O-rings or ripped seals anywhere. Everything looked almost brand new. All of the jets were clean too. Floats were fine. Advice to anyone doing a carb rebuild, disassemble them first before ordering parts. I could have saved $240 had I waited. The $270 rebuild kit from CPS will work just fine unless you need floats. We ended up replacing the floats and float bowls for good measure to the tune of $711 total for all the parts. 

The mechanic will be syncing the carbs and adjusting the throttle/choke cables today and hopefully if the weather stays good a test flight.