Carb Balancing

I would personally try to get a more exact balance at the 3800 rpm rather than 2000 rpm. The engine spends way more time at the higher rpms.

By the way, where did you get that nice set of mercury manometers? Much better than vacuum gauges. I have been looking for some.

Coincidentally I was about to ask a similar question re 912ULS.

Had my first attempt at balancing - with gauges - yesterday. Found it quite tricky and variable. No doubt there's a knack that comes with practice.

Anyway I got it to around 1" at 4000 varying another inch or so while reducing revs, is that OK? However at idle, which I set manually beforehand, it was more and I had to increase one idle stop and reduce the other quite a bit. Is this normal please? It does idle smoothly now at about 1700.

Thanks.

Yes that is fairly normal; balance at idle is done by adjusting the idle stops. After you come off the idle stops, the adjustment is done with throttle cable position. The two adjustments are separate, but I believe it is better to do the idle stop adjustment last.

The manometer is called "Carbtune Pro". I also have a digital Carbmate. I like the monometer better. I have been told that balancing just off the idle stops is most important. Higher RPM are more smoothed by the balance tube when everything is reconnected. It is an art i"m learning. Seems to me a vernier or some sort of fine tune thumb wheel adjustment device at the carb / cable connection would be great. 

Thanks for the manometer info.

Regarding balance rpms, Roger, one of the long time Rotax experts on this Rotax-Owner forum, strongly recommends doing your carb balance at 3500 rpm, which is somewhat different than the Rotax maintenance manual instructions. The engine intake crossover tube has a harder time compensating for out-of-balance at high rpms because of the higher intake air flow, so it makes sense to me to balance at higher rpms. A precise balance at 3500+ rpm always seems to hold pretty well down to 2000 rpm.