912 ULS rough running at 2350 to 2450 rpm

So, are you saying that you had the rough runnign problem before the carb rebuild but it was worse afterwards? What components did you change and what adjustments did you make?

Hi Allen,

Check for:

Throttle cable binding 

Propeller balance

Engine mount rubbers fatiguing😈

Hi Kevin and Sean.
I have taken the carburetors apart again to check, but everything looks ok.
I bought the Rotax rebuild kit and replaced everything except the throttle o-ring. The brass bracket for the floats is adjusted and the floats are ok. The air/fuel screw is 1.5 turns out as prescribed. Mechanical adjustment has been done with feeler gauges, (with the spring pulling the throttle at idle) It runs at 1700 rpm. and runs well, but when I put the vacuum gauge (which is calibrated) on there is a big difference. I then re-install the throttle cables and have to adjust them to get the vacuum to be the same on the right/left side. The engine runs well from 1700 - 2300 and again from 2800 and all the way up. The vacuum is the same on both sides. But at 2300-2700 ish the engine shakes and runs rough. The vacuum is still the same on the right/left side.

The spark plugs on the right side are black, so I may need to adjust the air/fuel screw so it runs leaner, and it will be completely different than the left side. ? Or is there a clogged channel to the idle system?

Plug is ok, throttle cables are ok, engine rubber is ok.

Best regards Allan

Hi Kevin. 

Yes it ran a little rough in 2400- 2600 ish before renovation, but not much, It was a bit annoying that is why i did the renovation.

Maybe i should have used a ultra sonic wash ....

I doubt its a carburettor problem.

My engine runs a little rough around the same rpm band BUT only when cold and when I close the choke completely

When you say the throttle cables are OK - how have you determined this?

Is your throttle system control cable all the way or is it part rod?

You have not mentioned propeller balance?😈