912ULS Max Idle RPM

by Jospeh Kiefer in 912 / 914 Technical Questions 13 years ago

Rotax SL-912-016 specifies a maximum idle speed of 1800rpm (section 3.3). On the other hand. the Roatx Owners video on Carb Sync says to set the idle between 1800 and 2200rpm. Why the difference? Which is correct?

Re: 912ULS Max Idle RPM

by Roger Lee » 13 years ago

Roger Lee

129 5.31k 5.12k

Hi Joseph,

Both are correct it is just the way two different groups have written it up and it's just a range to fall in. With the high compression of the 912ULS at 10.5:1 you don't want the idle too low or it just beats up the gear box and other parts not to mention all the extra vibration throughout. A good place to be to set the idle is between 1700-1900 rpm when you are all the way pulled back to the idle stop in the cockpit. While sitting and idling to warm up or wait to take off then let it idle around 2000-2300 to make it smooth and easy on the system. Some of the idle setting depends a little on the individual plane. Some are very draggy and a little higher idle rpm is no big deal. Some planes are very slick with a good glide and these folks tend to set the idle on the lower side to make it a little easier to land. Setting the 912ULS down around 1500-1600 isn't good for it. It is a different story for the 912UL with a lower compression. It can be set a little lower because it isn't sitting there hammering on itself, but it is still better for that engine to idle around 1700-1900 too.

The bottom line is to make either engine run in a smooth rpm range while just sitting.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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912ULS Max Idle RPM

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