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912ULS Circlip Position

JFCRV12

Well Known Member
Curious with the colder weather coming (at least in northern latitudes) if anyone adjusts their circlip position on their 912ULS?

Or said differently, on what notch do people keep their circlip in summer/winter or elevation?
 
Pretty sure he means the little C-clip on the metering rod in the carbs. I don't change mine, it stays in the factory specified slot.

Of course I could be wrong.
 
Same position

I believe that the carbs compensate automatically for changes in air density e.g. due to altitude, temperature. So no need to disassemble and change the carb between seasons.
 
Bing Carbs are constant Velocity carburetors, and self compensating. No need to change main jet needle valve settings.
 
I believe that the carbs compensate automatically for changes in air density e.g. due to altitude, temperature. So no need to disassemble and change the carb between seasons.

They do compensate automatically, but you can 'bias' them towards more lean or more rich. There are 4 positions. The top is most lean and the bottom is most rich. Factory setting is the 2nd up from bottom.

I have read in the Rotax heavy maintenance manual that people change them to compensate for temperature extremes from hot summer to cold winter or after moving to somewhere with a very high elevation. The factory setting is done at 1000ft MSL I believe

In the midwest USA where summers are 100F degrees and winter can easily be -10F I would think moving the clip a notch at some point would be wise. I think I recall seeing a post from Vic Syracuse (in Atlanta) where he moves his one notch in the winter and back down a notch in the summer.

I'm inclined to leave it alone, but thought maybe bumping them a notch may result in a bit leaner mixture and even better fuel consumption/cleaner burn.

Anyway, just a thought and question to see if anyone has already given it a shot.

Here's a preview video on Rotax Owners to give an idea: https://www.youtube.com/watch?v=lDe1ilB1ZNI&feature=emb_logo
 
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As long as people don't screw with their engines, a Rotax will last forever. You're suggesting screwing with it. Don't assume you know more then the designers. Unless you only fly in Denver and NEVER get lower, don't screw with it.
 
As long as people don't screw with their engines, a Rotax will last forever. You're suggesting screwing with it. Don't assume you know more then the designers. Unless you only fly in Denver and NEVER get lower, don't screw with it.
Wasn't assuming. Which is exactly why I asked. Also, it literally says in the maintenance manual that you may need to change the carb circlip position to account for seasonal changes. This will be my first season owning a rotax powered plane. A recognized expert in Vic Syracuse stated in these forums that he changes his 2x per year (Sumner/Winter). Net, I think it's a valid question and smart to desire to understand our engines as much as possible.
 
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Valid question indeed!

Thanks for asking it. I learn stuff from other’s questions that I haven’t thought of yet!
 
Curious with the colder weather coming (at least in northern latitudes) if anyone adjusts their circlip position on their 912ULS?

Or said differently, on what notch do people keep their circlip in summer/winter or elevation?

Go do a flight in the middle of winter, where ever you are, and when you land, pull the spark plugs and look at the color of them, and then decide where your fuel mixture is on the scale.
 
The cir-clip position

At 400 hours I solicited help on my carb inspection by finding an old school carb guy in the Denver area. We talked about and reviewed the condition or sootiness of my plugs and decided to move the needle cir-clip to the third position. I haven’t had a need to check the plug condition now at 465 hours.

Starting and normal operations through the summer have been good, fuel economy the same as always, and my hope is for cleaner looking plugs. Annual happens January into February and I will change all the plugs then, and will document their condition.

I don’t think I would changed the cir-clip position had I not gotten guidance from someone having a lifetime of carb knowledge. He didn’t have any Rotax experience but was very familiar the Bing carburetor.
 
At 400 hours I solicited help on my carb inspection by finding an old school carb guy in the Denver area. We talked about and reviewed the condition or sootiness of my plugs and decided to move the needle cir-clip to the third position. I haven’t had a need to check the plug condition now at 465 hours.

Starting and normal operations through the summer have been good, fuel economy the same as always, and my hope is for cleaner looking plugs. Annual happens January into February and I will change all the plugs then, and will document their condition.

I don’t think I would changed the cir-clip position had I not gotten guidance from someone having a lifetime of carb knowledge. He didn’t have any Rotax experience but was very familiar the Bing carburetor.

Your base altitude is at 5400 ft elevation, and you only go up, from there, though if you travel distance, you may go down if you head towards the Mississippi river. Someone closer to 500 to 3000 ft AGL for base operations should probably leave their circlip setting alone, so that they don't run too lean on the main jet, which is pretty much where the 912 ULS runs above 4500-4800 rpm's.
 
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If I remember correctly the intake runner lengths and differences in curved shape cause the back cylinders to run rich at idle. This is what you are seeing on the plugs when you shut down the engine after taxi back to the hanger and not indicative of operation at cruise power.
 
In the midwest USA where summers are 100F degrees and winter can easily be -10F I would think moving the clip a notch at some point would be wise. I think I recall seeing a post from Vic Syracuse (in Atlanta) where he moves his one notch in the winter and back down a notch in the summer.

Luckily in the Ohio, we rarely see temps at those extremes and on the rare occasion that we do, then we probably aren't flying anyway. I just keep my positioned at the factory setting and the Rotax does just fine.

Flying RV-12 (170+ hrs and Oshkosh 2019)
N418MJ
Warren County, OH (I68)
[email protected]
http://www.mykitlog.com/mwjohn63
https://www.youtube.com/watch?v=EJdXcjckN6M
2020 dues paid
 
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