Anytime you do any adjustment to the carbs the gauges should be on. One carb may be more influential for what you are trying to accomplish. Trying to just adjust the idle lower without the gauges will most likely put them out of sync.
Many people have varying likes and dislikes for setting their idle rpm so some of this become personal preference. Too high an idle can make you drag your brakes constantly during taxi or too high an idle may make the starting sequence different to keep from flooding. You can set it for something like 1650 so long as you know not to ever just sit there at that low rpm in a 912ULS with its 10.8:1 compression and let the gearbox bang around. Always best to warm up or sit and idle at 2000 or better. The lower 1650 rpm is better suited for pulling back to idle for landing (personal preference here because the stick actually controls the speed not the throttle) or just when you get ready to shut the engine down pull it back to this lower idle and then turn the mags off.
So you may get differing opinions here on a good idle rpm number, but it's not an exact number, but it is within an rpm range that suits your needs, likes and specific aircraft.
Roger Lee LSRM-A & Rotax Instructor & Rotax IRC Tucson, AZ Ryan Airfield (KRYN) 520-349-7056 Cell
I agree with Roger
Something like 1650 to shut the engine down is good but don´t forget to maintain the engine running at about 2000 or more during warm up and taxing to preserve the gearbox.
Paul -- I concur with Roger's suggestion of a 1,650 rpm idle speed. That is what Van's Aircraft recommends for the RV-12 with the 912 ULS and it works very well for my operations. As Roger says, don't let it go much below 1,800 - 2,000 rpm for any length of time. Active observation and management of the throttle / RPM by the pilot is a very useful habit with the ROTAX. -- David
When I left the hangar yesterday everything seemed great, engine sounded good at all speeds, no leaks but when I went back today to recheck the idle speed everything started up nice, 2000 rpm for a couple of minutes then 2500 to get the temps up.... after about a minute there was fuel venting out of the float valve again and some small vibration that wasn't there yesterday.
I suppose I have to put it back on the gauges but it all looked good when we left, seems odd that it would change overnight though I wonder if it is more to do with how warmed up the engine was yesterday by the time we were done as opposed to the 'cold' start today. I say "cold" because it is 92F out.
Any thoughts on the float valve? Still a vibration issue?
I may have to see if the FBO mechanic can do something but I doubt they've seen a Rotax any more than I have.
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