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Engine failure RV-12

Felix1973

Member
Hello fellow RV-12 pilots:

Yesterday I had an engine failure right after takeoff. I turned around, declared emergency and landed her safely. It was pretty scary though.

https://drive.google.com/open?id=1yjPmp4QFDlpFBanzNlJ0NIHiLoh4B4FQ

This happened at 300ft and all engine instruments were in green. I did do pre-flight and run-up and had no prior indication for that. Ambient temperature was 82 degrees with 70% humidity. I am running 93 auto-gas.

I uploaded a short video of that incident I would like to get your feedback, maybe anyone can determine from sound of the engine what kind of failure this may have been?

Thanks
Felix
 
Did the engine run normally after landing (and catching your breath?). If so, could you do a full-power run-up?

Fuel starvation/flooding (vapor lock due to winter blend gas or flooding due to a defective carb float?) is a likely suspect. Other than a bit of hesitation in turning back.....well done!

But anything we suggest is secondary to a thorough visual and operational inspection of the engine and data from the engine monitor.
 
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Thanks for your feedback Sam. Yes, the engine ran fine after landing and no, I did not yet do a full-power run-up after yesterday's incident.

I had 16 gallons fuel in the tank and was climbing at Vy (75kts). Any idea what might have starved the engine from fuel in that situation?
 
Thanks for your feedback Sam. Yes, the engine ran fine after landing and no, I did not yet do a full-power run-up after yesterday's incident.

I had 16 gallons fuel in the tank and was climbing at Vy (75kts). Any idea what might have starved the engine from fuel in that situation?

Anything I say is mere internet speculation but if the engine performed well before and after the incident one possibility is vapor lock due to winter blend auto gas on a warm day. I've had this happen with a Lycoming engine in the RV-6 but don't know if RV-12ers see this as a concern with the Rotax using winter Miami gas. Obviously any filters in the fuel system need a very careful examination.

Did you build this aircraft? If not, who maintains it for you? Do you have access to local Rotax experts or RV-12 pilots? What do they suggest after looking at your engine?

By the way....welcome to the VAF community....wish it was under better circumstances! :)
 
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First,

Excellent flying!!!

My guess is fuel related.

While I have very low time flying, I do have considerable experience with engines. I would suggest you check all fuel filters, fittings.

I watched the video, it was hard to tell, but it seems like the engine continued to put out sporadic power almost till the end. Is that true.

On a secondary note, I would check all ignition wiring connections as well.

For us who are curious, it would be helpful to know some more details likeL
Engine Make Model,hours.
Fuel system details, Pumps, how many? Return lines?
Fuel, 100LL, Auto?
Time on the system flying.
Electrical. Mags? Dual? Aftermarket?

Please keep us posted.

Charlie
 
A question for RV-12 pilots....is carb ice a concern with the 912?

If so, 82*F @ 70% is prime conditions:

carb_ice.gif
 
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A couple years ago I had the same thing happen after takeoff in my RV12. The engine was warm and I had just filled the fuel tank to the top of the filler neck.

The taxi out was short and takeoff was normal until about 500 feet when the rpm rolled back. I realized that I was high to land so I chopped the power and landed uneventfully in the opposite direction.

After landing, the engine ran perfectly with full power and no stumbling. I checked the carburetors and floats and all was fine. Fuel pressure normal.

The fuel used was Swift 94UL.

In this case possibly fueling to the top of the tube might have had something to reduce fuel venting. Or short taxi with warms fuel.

Mitch757
 
It sounds like the engine was making partial power or at least at times it was? Is that true? Hard to tell from video. Glad you made it back around. These occasional examples of people making the impossible turn possible could lure folks into trying to pull it off when it happens to them. The being said we as pilots need to try and learn the details of what made it possible so we can use that knowledge if it ever happens to us. We also have to realize that not all RV's are the same anymore. The 12 likely has a much different glide ratio than a RV6 and trying this same turn in the same situation could end much differently.

At this point it looks to me like the partial power helped make this turn possible. Would love to know what the situation was in reality.

Would also love to hear what your thoughts were. Looks like there was some hesitation at the beginning which is perfectly normal. What made you decide to turn back?

Engine failure early in the takeoff climb is one of my biggest fears in flying.
 
Engine Failure

First of all glad you're ok. 300 feet and a turn back to land. I was always taught that is a recipe for disaster. The classic stall spin to the ground. I know I wouldn't get away with that in the 4. Is this something that is safe in the 12?
 
First of all glad you're ok. 300 feet and a turn back to land. I was always taught that is a recipe for disaster. The classic stall spin to the ground. I know I wouldn't get away with that in the 4. Is this something that is safe in the 12?

It was in this case. :)

Makes a big difference when the engine is still producing some power....and the -12 is a different aircraft from the -4.
 
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Felix,

Very early in my flight testing I had a similar incident with my 912ULS powered RV-12. In my case, at around 300 feet during a 65-70 knot climb out, the RPM's went instantly from 5,200 to 4,000 accompanied by some roughness and a small whiff of fuel. I pulled the throttle out and eased it back in and the engine started running rough again if the RPM were much above 4,500 so I kept the power around 4,000 and told the tower I had a partial loss of power. I was able to easily make it around to an intersecting runway for a safe landing.

Using Savy Analysis, I was able to determine the left carb went rich at the time of the incident accompanied with a small drop in fuel pressure and small increase in fuel flow ... because the EGT dropped on the left side. Removed the left carb ... floats checked OK, needle valve looked good, so then flushed the carb/fuel line using the electric fuel pump. Only found one tiny speck of crud ... which I'm assuming got caught under the needle valve causing the carb to go rich. Have not had the issue since.

Suggest you save the data file from your SkyView and use Savy to chart out the data ... the charts will show you if you went rich or lean based on what happens to the EGT.

Since auto fuel is being used and you are in a warm part of the country, I'll pass on what I've been doing with good results. In the spring when the temps here begin to get into the 80's if there is still only winter blended fuel available at the pumps, I mix in some 100LL (at least 30%) until the summer blend fuel is available. This seems to really lower the possibility of vapor lock issues due to the combination of winter blended auto fuel and warm temperatures.

Good job on getting the bird safely back on the ground.

Happy flying,
 
I am not familiar with a rotex engine, however if you had an electric boost pump on, it should have over come a vapor lock.

Mike Hepperlen

You can't count on that. If fuel is boiling in the carb bowl or downstream of the pump(s), it can disrupt fuel delivery enough to reduce power or even stop the engine, even in a Lycoming. Been there...done that..... :)

Winter blend auto gas is fickle stuff.....I don't like it.
 
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well done

I will let your research figure out the engine problem, but the flying was superb. Nice bank angle and pitch control. I am in the camp that pilots/owners should try this out now and then to determine the altitude needed for success. I have put it to use in a Luscombe, Cessna 210 and an RV9A. In the case of the RV, I only turned 90 degrees left to use the intersecting runway end. (rain water in fuel)
Training in advance is always a good thing. Well done sir!
 
Before you do anything drastic, pull the float bowls. If you see debris then I bet that is what caused this problem.

Similar happened to me in my CTSW. A piece of debris can pick up causing a partial power loss.
 
The (im)possible turn

Congrats and well done on getting it safely back on the ground. Here?s a link to a webinar of Brian Schiff talking about ?The Possible Turn? on the NAFI website. At some point after takeoff, it becomes possible to make it back to the airfield. He describes how to figure out that point and how to practice. He also describes when not to turn back. Cheers.
https://www.mentorlive.site/program/20.html
 
210/30 turns from failed departure

First of all glad you're ok. 300 feet and a turn back to land. I was always taught that is a recipe for disaster. The classic stall spin to the ground. I know I wouldn't get away with that in the 4. Is this something that is safe in the 12?

All: I know the mantra: engine failure on take off, land straight ahead and hit something soft. I submit that that is certainly good advice about a Cessna, Piper or other conventional spam can. And landing straight ahead at 1.3 VSO beats stalling 200 feet in the air.

And some sacrilege: my 1986 RV4 wood prop (no constant speed disk drag) has a wing loading at gross of 13.6 pounds; a power loading of 9.3 pounds per hp; and a pretty high roll rate. At a typical climb speed of 85kts, it is about 40 kts over stall speed...assuming 1.5 seconds to perceive and react, my strong sense is you can hit 300-400 feet, detect failure, roll, decel to 60 kts, do the 210/30 turns and get back to your lift off location. I know it can be done from 500 feet with plenty of excess altitude because I have done it with a vapor lock from an "all metal life time warranted fuel hose". I vividly recall rolling wings level on short final thinking how much energy and altitude I had left and how any other plane I had flown would have planted me in some trees or vineyards...What an amazing plane! 300 calls for some quick thinking, but those houses in front might be a pretty strong incentive to make a rapid 45 degree banked roll, drop the nose to maintain 60, drop full flaps, and worst case, park it on the airport property. most likely, you hit the runway, my guess.

The 4 has so much more performance than a spam can that the prescriptive rules really are different (at least for me). Not saying you cannot stall spin yourself: a partial list of people I knew personally who have done it in RVs include Arlen Pestes, Randy Pexton, Bill Bruce, Bill Paragin, Mack Johnston...and you can land straight ahead into a car/house/tree/powerline and have the same outcome. I think the best thing to do is focus inside plane because the physics variables are pretty baked in the cake: maintain 60 kts till you are out of the steep turns, wings level, slow to 50 kts and hope there is runway under the wheels.

So, we know from this video that an RV12 with a somewhat delayed response and maybe a little residual power can make the 210/30 from around 300 feet. I know my 4 can do it from 500 when it is fat with fuel and bodies, and starting from a 85 kt climb. Not interested in starting a fight about one of the sacred cows of light plane operation. Maybe it is the case for the majority of pilots in the majority of spam cans, park it straight in front is the best advice. MTCents J
 
Going to drift just a little from the thread, but.
My last BFR was done by a USAF AWACS E3 pilot (also a CFI), at night in our C-150.
He "studied" the wind and determined we could practice engine outs at 500', on take-off, with return to the runway. We/I did several of them, and I got pretty good at it myself. It is possible, under certain conditions, you just have to PAY ATTENTION to what you're doing.
 
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You where lucky that wasn't a full on engine failure, the video would be in the hands of the coroner!
Obvioisly a fuel supply issue, remember our engines are mechanical contraptions, they WILL fail at times!
Hope you get to the bottom of the issue.
 
My dad had the same thing happen to him with the -3. The problem was that a dirt dauber decided to start a nest in the vent tube. The engine ran fine on the ground, but when power was applied there was not enough vent to keep fuel flowing. Cleaned out the nest and everything was fine. Just my $.02.
 
Turn Back decision.

Congrats and well done on getting it safely back on the ground. Here?s a link to a webinar of Brian Schiff talking about ?The Possible Turn? on the NAFI website. At some point after takeoff, it becomes possible to make it back to the airfield. He describes how to figure out that point and how to practice. He also describes when not to turn back. Cheers.
https://www.mentorlive.site/program/20.html

First, excellent job by the OP by getting the plane on the ground safely under a very stressful situation. Second, thanks for posting your experience for the rest of us to "Armchair Quarterback". I suspect this situation happens more than we think, but rarely hear about them. Thanks again for sharing!
It appears the decision of the OP to turn back is met with mixed reviews. However, after watching the video posted in the link above it appears that under certain circumstances the turn back may be an option and sometimes the best decision.
The OP made it safely back to the runway, so it was obviously the best choice in this situation. Watching the cockpit video, it appears he was departing over a densely populated residential area. Had he made the rash decision to land straight ahead, we would likely still be watching it on the news.
As described in the video by Brian Schiff, every takeoff is different and requires different actions in the event of an engine malfunction. For the turn back, the key is knowing the parameters required to do it safely. If the parameters aren't met, then straight ahead may be the only option..trees, residential area, or not.
Probably needs to be another thread, but it would be interesting to see some of the turn back data described in the video for the different RV models.
 
[Begin moderator mode]

The original poster is seeking input on why his engine lost power. It would be more appropriate for "turn back" posts to be in a different thread so the response to the inquiry by the original poster won't be lost in the noise. The OP is a newcomer to VAF, lets not swamp his first thread with our renowned ability to drift. Thanks.

[End moderator mode]
 
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?carb float

I had a similar take off in my rv-12. Sudden loss of power and hard to make it back to the runway. It was a bad carb float (leaky sunken float), so I would agree with weighing both carb floats. Good luck. Quite scary when it happens.
 
Before you do anything drastic, pull the float bowls. If you see debris then I bet that is what caused this problem.

It is fully possible for there to be FOD contamination in one or both of the carbs and not fins anything in the float bowls.

This has been the cause of quite a few difficult to troubleshoot 912 ULS engine problems.
 
I had a very similar issue happen to me in my RV12, engine went from full power to partial as I was in climb out.

I took the bottom of my carbs apart air cleaned everything out, swapped out all my fuel and it happened to me again.

I then focused on the top of the carbs, I took the pistons out, cleaned them thoroughly and lubed them with oil. I had noticed that the carb pistons felt a little “rough” when moving them up and down prior to cleaning and lube. Post clean and lube very smooth in their bore.

Since that have had zero issues. I really think my partial power was an out of balance situation caused by the dirty pistons. Savvy analysis would support this as the EGTs separated by a couple of hundred F

I also realized that when doing the ignition check before I had seen the rpm move around in the range a lot more when trying to hold 40000 rpm I am conscious of that and to really check my EGTs on run up.
 
Does the RV12 have a return fuel line? Kitfox factory and Rotax both recommend a return fuel line, (carbs) I have heard stories similar to this on Rotax airplanes without the return line installed. David
 
Fuel Contamination?

I previously worked the line at an FBO. The fuel training and handling for 100LL is strict. Off the dedicated tanker (only hauls 100LL) it's filtered as pumped into fuel farm tank, filtered again into the fuel truck, then filtered as it's pumped from the truck into my airplane.
I used to "save" money by using five gallon cans to get mogas at the gas station and drive to the airport to fill up the plane. The engine and plane were approved for mogas.
During an annual my A&P pointed out that the only protection I had was a finger screen. As an exercise we poured fuel from one of my cans through a coffee filter. It was pretty scary how much debris was caught. I'd bought the cans new and only used them for the plane.

My A&P also ran the FBO, he pointed out that- YES 100LL is more expensive. IT's also filtered and tested more often than mogas. After that I was happy to buy 100LL. Just my 2 cents. I'd be interested to know what you find.
 
There are good reasons why mogas is recommended by the manufacturer for the Rotax engines. I've used mogas off and on in the RV-6 for over 15 years and ALWAYS use a Mr. Funnel when transferring mogas from the 5-gal can to the wing tanks. This funnel has a filter so fine it will capture water molecules and eliminates the possibility of contamination from the fuel can.

Highly recommended for our RV-12 pilots even though some ingenuity will be needed to adapt it to the RV-12 fuel filler.

https://www.aircraftspruce.com/catalog/appages/fwfunnels.php

05-01055.jpg
 
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Repeating what someone else said for emphasis... you should download and save the datalogs from the SkyView, and then look at them using SavvyAnalysis.

-Robert
Dynon
 
filtering doesn't have to be limited to the airport avgas. it's up to you. i wouldn't ever dump into my tanks without a filter. i dump into a 55 gal drum that has an electric pump and a filter in the line.
it's not a few pennies, it's a buck a gallon.
 
I hope folks have another filter in their system besides the finger screens in the tanks. If not, you're asking for trouble at some point.
 
Know thy aircraft

...

1. The best thing we can do is to become proficient in our aircraft in MANY situations. Rarely do we have black and white decision points. We can tell ourselves that we?re going to land straight ahead, plus or minus 30 degrees, but what if... (a) the best place is 35 degrees off our nose; (b) the engine is making a little power; (c) plus or minus 30 degrees puts you into a schoolyard full of kids; etc. etc.

...
Could not agree more - and with the rest of your post.

Coarse rules like "never turn back" are good for many situations, and if you had to choose between "always turn back" and "never turn back" of course the latter is what you would tell someone undergoing instruction.

It's a bit more subtle and a lot more work to say "know your aircraft" and "fly it right under all circumstances" - but this is really what we should be doing.
 
Yikes!

First of all, a welcome to new member "korbike" as I see this is your first post.

At first Felix, I could not see your video as the number of playbacks were exceeded so I hit "download' and that worked.

Boy! Even knowing the outcome that gave me some pucker factor just watching it.
 
Could not agree more - and with the rest of your post.

Coarse rules like "never turn back" are good for many situations, and if you had to choose between "always turn back" and "never turn back" of course the latter is what you would tell someone undergoing instruction.

It's a bit more subtle and a lot more work to say "know your aircraft" and "fly it right under all circumstances" - but this is really what we should be doing.

"Always stop for a yellow light" during Drivers Ed slowly becomes "well, sorta, sometimes" in real life as experience grows and judgement is applied. And sometimes we still get it wrong...
 
Eerie

Your video was almost exactly what I faced a few years ago. Similar climbout, houses below. Passenger. Same turnback to land on the runway.

In my case it was a broken crankshaft.

Glad you're ok. Your video really creeped me out and brought back some memories.

- Pat
 
One of the Tecnam P2006T (twin Rotax) we had in the UK suffered one engine running rough in the climb. It was repeatable when in the climb attitude.

We found a very small piece of orange FOD in one carb float bowl which looked like it was possibly from the fuel line. Once the float bowl had been cleaned, the fault never reoccurred.

On a Tecnam P2002-JF (single), it suffered rough running at low to medium rpm on the ground, fine above medium rpm. Whilst I was running it, it cleared and I suspect that something was blocking the idle jet orifice in the float bowl but eventually got sucked through the system. Fault never reoccurred.

Whenever I had the float bowls of our 12, I checked to make sure they were scrupulously clean and that the idle jet feed was clear, by tilting the float bowl with fuel in watching that feed area filled and emptied.

One other thought that perhaps Scott may have experimented with. With a rough running 'fuel-starved' Rotax, has anyone eased the choke out to effectively richen the fuel mix and get it to smooth out? Just a thought.
 
Hello fellow RV-12 pilots:

Yesterday I had an engine failure right after takeoff. I turned around, declared emergency and landed her safely. It was pretty scary though.

https://drive.google.com/open?id=1yjPmp4QFDlpFBanzNlJ0NIHiLoh4B4FQ

This happened at 300ft and all engine instruments were in green. I did do pre-flight and run-up and had no prior indication for that. Ambient temperature was 82 degrees with 70% humidity. I am running 93 auto-gas.

I uploaded a short video of that incident I would like to get your feedback, maybe anyone can determine from sound of the engine what kind of failure this may have been?

Thanks
Felix
I had a similar problem on take off in my 12. I was able to return to the runway under a decreased power setting and level flight. This occurred in warmish weather and after doing a few touch and goes with the engine at full normal running temperature.

I retested the run up once on the ground. Standard run up was fine, however, full power showed the flaw and destroyed my fuel sensor. (High fuel pressure) My hose to the fuel pressure sensor was in contact with the radiator hose which caused the winter blend fuel to boil. I found fuel on the sensor ware the plastic and brass meet.

This may not be your problem or help you, but it is something to check.
 
First of all, a welcome to new member "korbike" as I see this is your first post.

At first Felix, I could not see your video as the number of playbacks were exceeded so I hit "download' and that worked.

Boy! Even knowing the outcome that gave me some pucker factor just watching it.

Thanks for the welcome arrfguy, great site and group, just starting to get the RV bug!
 
You don't mention the age of the fuel. One time I filled for a trip that did not happen and with weather it was 3-4 weeks of rain until I flew. At 5000' I had one carb blocked and got in some glider time back to the airport. Flushed with 100LL to fix. I used 100LL for winter or when I would not be flying weekly from then on. Other possibility- a few have had starvation in climb out from having the tank overfilled. Fuel appeared to block the new style filler tube vent. Mine would show reduced pressure in climb out with Dynon Betty yelling about low fuel pressure. Drilling a hole in the filler cap (like the original) as a backup fuel vent took care of it.
 
Your video was almost exactly what I faced a few years ago. Similar climbout, houses below. Passenger. Same turnback to land on the runway.

In my case it was a broken crankshaft.

Glad you're ok. Your video really creeped me out and brought back some memories.

- Pat


On a new motor E-LSA RV-12? How many hours on the engine? Or was it an E-AB motor not bought through Van's?
 
There are good reasons why mogas is recommended by the manufacturer for the Rotax engines. I've used mogas off and on in the RV-6 for over 15 years and ALWAYS use a Mr. Funnel when transferring mogas from the 5-gal can to the wing tanks. This funnel has a filter so fine it will capture water molecules and eliminates the possibility of contamination from the fuel can.

Highly recommended for our RV-12 pilots even though some ingenuity will be needed to adapt it to the RV-12 fuel filler.

https://www.aircraftspruce.com/catalog/appages/fwfunnels.php

05-01055.jpg


I use a dual filter version on that funnel, I never put fuel in my RV's wings unless it's thru my funnel, peace of mind even though it's a pain and I get odd looks when fuelling!
 
Investigation part 1

Hello and thanks everybody for the input so far.

Today my mechanic did the first steps in the investigation:


1) Spark plugs: Dirty, we changed all of them.

https://photos.app.goo.gl/FCBgu6razKGMTsTK6

2) We looked into the cylinder: No damage from potential detonation.

https://photos.app.goo.gl/zhhho6WCFMtP52DS7

3) Gascolator: clean.

4) Carburetor:

Left side: One float was lower than the other.

https://photos.app.goo.gl/D7vkeF8mQ8snAi4c8


Right side: Float bowl was connected with piece of rubber to the heat shield underneath (why?):

https://photos.app.goo.gl/THHMjWpXqvwy2LWv8

https://photos.app.goo.gl/f5f9cGWWWUgM3CLHA


5) We then looked at the blackbox data at the time of the incident (at second 30) and observed EGR temperature on the right to plummet.

https://photos.app.goo.gl/HFFD4v5S8GAEGmgRA

Does anybody have any thoughts on a root cause and the purpose of the rubber piece?
 
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The piece if rubber is fuel tank sealant which Vans specify to put between the float chamber and drip tray - presumably to damp vibration.

I think your problem is that the right cylinders have seen a very rich mixture (hence the black spark plugs) because you most likely have one heavy float which has allowed the carburettor to flood.
 
One of the Tecnam P2006T (twin Rotax) we had in the UK suffered one engine running rough in the climb. It was repeatable when in the climb attitude.

We found a very small piece of orange FOD in one carb float bowl which looked like it was possibly from the fuel line. Once the float bowl had been cleaned, the fault never reoccurred.

On a Tecnam P2002-JF (single), it suffered rough running at low to medium rpm on the ground, fine above medium rpm. Whilst I was running it, it cleared and I suspect that something was blocking the idle jet orifice in the float bowl but eventually got sucked through the system. Fault never reoccurred.

Whenever I had the float bowls of our 12, I checked to make sure they were scrupulously clean and that the idle jet feed was clear, by tilting the float bowl with fuel in watching that feed area filled and emptied.

One other thought that perhaps Scott may have experimented with. With a rough running 'fuel-starved' Rotax, has anyone eased the choke out to effectively richen the fuel mix and get it to smooth out? Just a thought.

In another thread in 2014 Cactusman referenced an article in RVator about this (use of Choke), but that article seems to no longer be available.
Post is below.

http://www.vansairforce.com/community/showpost.php?p=937590&postcount=2
 
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This is mostly likely an indication that your carbs went out of sync at that point, given that one carb stayed at expected EGT I would say it?s safe to say that you don?t have a fuel system to the carbs problem. But that you most likely have a problem in the carbs.

I would check that you are getting unrestricted fuel flow through both carb fuel inlets - taking of the foot chamber cover and running the electric pump and measuring fuel flowed in the same amount of time (eg one minute) and comparing the carbs can give you a good understanding of that.

This is highly likely a restriction in fuel flow, which is either in the carb fuel inlet channel, between the seat and the needle valve. Or contaminants in the fuel bowls and/or in the main jet system.

I would also thoroughly clean and lubricated the pistons on each of the carbs and ensure that they are aligned properly ( the rubber gasket has alignment tabs, you and also feel alignment through the inlet throat of each carb.

Additionally I would ensure that you have no cracks in the rubber mating flange (carb to inlet manifold). And check that no leaks are possible on inlet side.

It?s also likely that you can replicate this behavior or at least see it in data you load to savvy analysis by running your engine at WOT on the ground. If a problem exists you will see the EGTs separate (a 40 F difference seems to be normal on most 912ULS I have seen).
 
Felix,

If the right side EGT plummeted at the time of your incident, for sure the right side of the engine went rich.

There are only a few things that can contribute to one carb suddenly going rich while the other carb is seemingly just fine.

1. The most likely suspect - one or both of the floats in the right carb have absorbed fuel and are heavier than the published Rotax specification of 7 grams for the pair, causing high fuel levels in the carb bowl, which floods that side of the Rotax engine with fuel.

2. Issue with the needle valve/seat assembly. A piece of crud may have made its way to the needle valve and got stuck between the needle valve and brass seat at the fuel inlet to the carb bowl. Remove the float arm and needle valve and do a close inspection of the needle valve and brass seat. Turn on the master for a few seconds and flush fuel through the carb. Reinstall the needle valve and float arm assembly. Turn the master back on and verify that raising the float arm will easily shut off the fuel with very little pressure needed on the float arm.

3. The float arms are not level – this will contribute to incorrect fuel level in the carb bowl … can be checked by eye … but best to use the Rotax tool/gauge that is used in conjunction with feeler gauges for making an exact adjustment.

4. High fuel pressure - negating the needle valve’s ability to stop fuel from entering the carb bowl. (Unlikely in your case, I should think, because only one carb went rich).

5. A mis-adjusted carb choke on the right carb. Make sure the choke on the right carb is sitting firmly on the metal stop when the choke lever is full in and locked. Verify the choke lever actually locks and holds the choke lever assembly on the stop.

The above five potential issues are the most likely causes of a carb going rich.

Let us know what the outcome is.

Happy flying,
 
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