Rotax High Altitude Mid-Range and Idle Mixture Settings

[Vantastic12]

The initial running of my Rotax 912 ULS at my home airport (KPSO) Colorado, at 6,700 feet MSL indicates a rich condition as indicated by eight velvety black spark plugs and a significant RPM drop on at least one of the two electronic ignition systems.

The tech at Lockhart Aero advises to adjust the mid-range needle valves adjustment, factory set at the third notch down from the top, up to a leaner condition in a higher notch toward the top of the needle, thereby lowering the needle into the jet. I moved it up one notch. The tech also advised not to bother adjusting the idle mixture screw from it's factory setting, one and a half turns out from the bottom, as it won't make any difference and "All Rotax 912 ULS's are set there."

However, the Rotax Maintenance manual says that turning the idle mixture screw in leans the idle mixture and turning it out richens the idle mixture. I'm in a quandary as whether or not to adjust the idle mixture screw from it's factory setting or not.

Any high altitude RV-12'ers out there with experience in adjusting the idle mixture screw from the factory setting?

[kkmarshall]

Just count the turns in till the idle screw seats and if it is at 1 1/2 then write that down. Now you can try any setting you wish to see if it helps. You can't hurt the engine at such low speeds no matter how you set it.

Keith

[vic syracuse]

Changing the ring on the needle so it changes the mixture helps a lot. I flew a couple of 912's on my kitfoxes for about 1200 hours in Atlanta over about 9 years. I actually changed the needle valve by one position for winter or summer. It really made a difference.

Vic

[Vantastic12]

Thank you for your input. I'm just going to run the Rotax with the mid-range mixture needle lowered (leaned) one notch and the idle mixture screw turned in slightly from the factory one and a half turns out, see how it runs/idles and tune from there for our 7,663' MSL field elevation.

Thanks again.

Vantastic12