Rotax RPM at Idle

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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Paul_G
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Location: Chelan, WA

Rotax RPM at Idle

Postby Paul_G » Fri Apr 13, 2018 4:40 pm

Today my flight instructor questioned the idle speed of my Rotax 912 ULS. He noted (correctly) that it was running between 2200 to 2300. I thought is was previously at about 2000 - but I'm not sure about that.

If it does need to be reduced, is that a big deal for me to make that change?
Paul G
N400TL 2016 Sirius TL-3000
Chelan, WA (S10)

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FastEddieB
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Re: Rotax RPM at Idle

Postby FastEddieB » Fri Apr 13, 2018 4:55 pm

1) That sounds high. High enough it will cause a lot of float down the runway when trying to land.

2) I think most are happy with an idle speed of between 1,600 and 1,800 rpm.

3) If it changed on your plane, there's got to be a reason - cable not seated the same, choke part way on, that sort of thing. Worth checking out.

4) You cannot legally change your idle setting unless you are an LSRM or better, or certified Experimental.

5) When changing the idle rpm, probably best to do a carb sync at the same time.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
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drseti
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Re: Rotax RPM at Idle

Postby drseti » Fri Apr 13, 2018 7:53 pm

I'm willing to bet the RPM was properly set to 1700 RPM or so - during the winter! Come Spring, the bowden cables warm up, change length, and the idle speed changes. One should re-sync the carbs twice a year, at the changing of the seasons (i.e, Spring and Autumn).
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof. H. Paul Shuch, Ph.D., CFII, LSRM-A/GL/WS/PPC, iRMT
AvSport of Lock Haven
fly@AvSport.org
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roger lee
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Re: Rotax RPM at Idle

Postby roger lee » Fri Apr 13, 2018 9:17 pm

That idle rpm is too high and you'll just ride your brakes to death. Lower it down to around 1650-1700. You never want to sit at this low idle, but keep it up to around 2K, but the low rpm is good for approaches and when shutting down the engine.
You will need to put the carbs ion gauges to make this adjustment. There is NO way to know which carb has the bigger influence or which one to adjust without them.
Roger Lee
Tucson, Az.
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Paul_G
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Re: Rotax RPM at Idle

Postby Paul_G » Sat Apr 14, 2018 10:28 am

Thanks to each of you for your replies. I will be taking it in to my A&P for some adjustments.
Paul G
N400TL 2016 Sirius TL-3000
Chelan, WA (S10)


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