Page 1 of 1

Rotax RPM at Idle

Posted: Fri Apr 13, 2018 4:40 pm
by Paul_G
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?

Re: Rotax RPM at Idle

Posted: Fri Apr 13, 2018 4:55 pm
by FastEddieB
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.

Re: Rotax RPM at Idle

Posted: Fri Apr 13, 2018 7:53 pm
by drseti
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).

Re: Rotax RPM at Idle

Posted: Fri Apr 13, 2018 9:17 pm
by roger lee
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.

Re: Rotax RPM at Idle

Posted: Sat Apr 14, 2018 10:28 am
by Paul_G
Thanks to each of you for your replies. I will be taking it in to my A&P for some adjustments.