Idle Adjustment on Rotax 912 ULS

[Bartman1959]

Does adjusting the idle speed on the Rotax 912 ULS carbs affect the carb balance? My 912 idles a bit low, about the 1580-1600 range, and I want to increase it to 1800. Would adjusting the idle screws the same amount on both carbs have anything to do with the balance of the carbs?:confused:

[Av8r3400]

If you adjust to 1800, you will find your plane will float for extended distances and will be very difficult to land well. At 1800 rpm your engine will be making enough thrust to continue to fly in ground effect.

During decent you need to throttle back to steepen the angle of approach. Once on the ground add in throttle to get the engine to idle at the rpm you want it to.

IMO, 1600 is even a bit high.

[Bartman1959]

Doesn't that depend on how heavy my plane is and how my prop is pitched?

[rv9ralph]

Bartman,
If you read the Rotax-Owners forum, you will find threads about high idle make the aircraft float on landing.
Av8r3400 is correct.
Read the Rotax manual on how to adjust the carbs for manual synchrinization. The manuals are available at Rotax-Owners.com.

Ralph

[Av8r3400]

Sure it will to a degree, but unless you are so under pitched that the engine redlines at 80 mph, or you're way over gross, you will find 1800 will be too much. These planes just like to fly too much...

Setting the idle is easy. Just adjust the screws the same amount on each carb and it will hold sync.

[Bartman1959]

Thanks, I appreciate the info.

[Bartman1959]

Bartman,
If you read the Rotax-Owners forum, you will find threads about high idle make the aircraft float on landing.
Av8r3400 is correct.
Read the Rotax manual on how to adjust the carbs for manual synchrinization. The manuals are available at Rotax-Owners.com.

Ralph


Thanks Ralph, I appreciate it.

[Skipatrol]

I adjusted my idle stops due to high idle RPM. Then I went flying with my CFI, who pulled very hard on the throttle, enough to kill the engine twice on approach, you can watch video here https://youtu.be/BKmL57jKHfQ

It took me several times adjusting the idle stop to get it down to 1700 RPM, but I have to be careful not to pull really hard, because the stops will deflect enough to kill the engine.

[Av8r3400]

Then you have it about right... LOL. ;)