Recommended 912ULS Air Filter?

A possible explanation: A restricted air filter does not necessarily mean a richer mixture; it would act similar to restricting the airflow with the throttle. As you throttle back, the bing carb is able to keep the proper air/fuel ratio so it does not become richer. What may be happening is the restricted air flow thru the filter causes the pilot to have to open the throttle more to achieve the desired engine power level. This makes the engine work harder than necessary, raising the EGT's.

Hi all

The K&N has a very long history with Rotax.  It is a good workable filter if serviced correctly,  at the very least at the annual.  That said the filter is what is used at Rotax and the power ratings and performance were all done with this filter type.  Obviously there are different opinions and people look to 4 stroke automotive experience to compare, this however is not a valid comparison.  We do not have mass airflow sensors, we do not have crankcase ventilation, PCV, valves, all things that do not like oil impregnated air filters.  That said it is a proven filter for our application.  

A CV carburetor flow rate for mixture control is not an issue with a K&N.  I doubt the engine will run richer as the air flow dictates how much the throttle "slide" will rise based on the incoming air ambient pressure. (the slide is not physically connected to the throttle). One may see lower performance but I don't think you will see different EGT.  What may be happening to the report of the K&N lowering EGT is that the slide put the needle in a different position (perhaps richer) position relative to the RPM.  

Just my 25 cents worth of opinion. 

Cheers

Hi James,

This illustrated explanation of a how a Bing CV works may assist you;

https://www.youtube.com/watch?v=IBFq9nHVmks

😈

Follow up from my posts above...  I have a Rotax Airbox on my 912ULS.  RANS Aircraft has the K&N part # SN-2540 specified for the single air filter used with the airbox.  I think that the SN-2540 filter has been discontinued.  So, I called Lockwood and they said that the "Rotax-approved" replacement was the K&N RU-1710.  I was excited to know that, so I ordered 2 filters; however, I am just now discovering that the RU-1710 is not an "exact" replacement for the SN-2540.  The size and shape are different, but the main problem is that the inside diameter of the RU-1710 is not the same as the inside diameter of the discontinued SN-2540.  So, the RU-1710 will not fit onto the airbox plumbing that I have already installed.  Does anyone have any sources for the SN-2540 (perhaps overseas) or a functional cross reference with a flange that will fit over an aluminum tube having an O.D. of 2.50"?

Thanks,

Mike

You may be able to get some assistance from K & N.

Avoid divulging your enquiry relates to an aircraft application.

K & N Customer Service Info

Need a human?Call 1-800-858-3333 (M–F)10 am ~ 4 pm CSTEmail: tech@knfilters.com

 

😈