Rotax 912 ULS loss of power in flight

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

Moderator: drseti

User avatar
Warmi
Posts: 1002
Joined: Sun Oct 16, 2016 5:35 pm
Location: Frankfort, IL

Re: Rotax 912 ULS loss of power in flight

Postby Warmi » Fri Mar 20, 2020 9:05 pm

If I were you I would not take carb ice as my first answer. The way I understand it m it is basically “diagnosis by exclusion” since you cannot prove or disprove it happening.
Flying Sting S4 ( N184WA ) out of Illinois

Wm.Ince
Posts: 965
Joined: Sun Nov 17, 2013 3:27 pm
Location: Clearwater, FL

Re: Rotax 912 ULS loss of power in flight

Postby Wm.Ince » Fri Mar 20, 2020 9:34 pm

Concur with Warmi on this. Sounds like classic carb bowl debris.
Bill Ince
CTSW (E-LSA)
Retired Heavy Equipment Operator

User avatar
ShawnM
Posts: 613
Joined: Sat Nov 11, 2017 9:59 pm
Location: Clearwater, FL / KZPH

Re: Rotax 912 ULS loss of power in flight

Postby ShawnM » Sat Mar 21, 2020 1:15 pm

I drop my bowls quarterly to check the floats, I'm on my third set, and also have a look in the bowl for anything other than MOGAS. :mrgreen:

Dave C
Posts: 32
Joined: Tue Jan 15, 2019 5:33 pm

Re: Rotax 912 ULS loss of power in flight

Postby Dave C » Sat Mar 21, 2020 3:33 pm

Warmi wrote:If I were you I would not take carb ice as my first answer. The way I understand it m it is basically “diagnosis by exclusion” since you cannot prove or disprove it happening.


I am definitely not going to take off assuming it was carb icing. Perhaps it was, but like you said I need to eliminate the other possibilities.

User avatar
drseti
Posts: 6652
Joined: Sat Nov 28, 2009 6:42 pm
Location: Lock Haven PA
Contact:

Re: Rotax 912 ULS loss of power in flight

Postby drseti » Sat Mar 21, 2020 3:48 pm

ShawnM wrote:I drop my bowls quarterly to check the floats


That's actually required at every 100 hour inspection (maybe every four months for me). Quarterly is good!
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US

User avatar
ShawnM
Posts: 613
Joined: Sat Nov 11, 2017 9:59 pm
Location: Clearwater, FL / KZPH

Re: Rotax 912 ULS loss of power in flight

Postby ShawnM » Sun Mar 22, 2020 10:43 am

drseti wrote:
ShawnM wrote:I drop my bowls quarterly to check the floats


That's actually required at every 100 hour inspection (maybe every four months for me). Quarterly is good!


I may be a bit more anal than most and after 3 sets of floats in as many years.....I'm a bit "float" shy now. I have a short list of quarterly maintenance tasks I do to my SportCruiser and dropping the bowls to check the floats and for debris is one of them. It takes very little time to do and it's piece of mind for me. I also understand it's also part of my annual condition inspection.

I've never experienced "loss of power" because of the floats, just a rough running engine at times. Pulling the bowls to have a peek just lets me know there's nothing in the bowls that shouldn't be.

Wm.Ince
Posts: 965
Joined: Sun Nov 17, 2013 3:27 pm
Location: Clearwater, FL

Re: Rotax 912 ULS loss of power in flight

Postby Wm.Ince » Sun Mar 22, 2020 11:15 am

ShawnM wrote:I drop my bowls quarterly to check the floats

Not a bad idea at all. I think semi-annual bowl inspection would be fine.

Which tool do you prefer for syncing the carbs?
Bill Ince
CTSW (E-LSA)
Retired Heavy Equipment Operator

User avatar
drseti
Posts: 6652
Joined: Sat Nov 28, 2009 6:42 pm
Location: Lock Haven PA
Contact:

Re: Rotax 912 ULS loss of power in flight

Postby drseti » Sun Mar 22, 2020 11:25 am

Wm.Ince wrote:Which tool do you prefer for syncing the carbs?


I personally use the CarbMate (about $180 at Aircraft Spruce), but analog gauges work just as well.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US

3Dreaming
Posts: 2777
Joined: Sun Jan 10, 2010 6:13 pm
Location: noble, IL USA

Re: Rotax 912 ULS loss of power in flight

Postby 3Dreaming » Sun Mar 22, 2020 11:41 am

First I should state that I have not used a Carbmate. I use analog gauges. It gives me a good idea of how much change needs to be made to correct the imbalance. Also by using this information along with watching the idle speed I can determine which carb I want to adjust, and which way I want to adjust it.

Wm.Ince
Posts: 965
Joined: Sun Nov 17, 2013 3:27 pm
Location: Clearwater, FL

Re: Rotax 912 ULS loss of power in flight

Postby Wm.Ince » Mon Mar 23, 2020 3:09 am

Thanks to both of you.

One other question . . . on the top end, what RPM do you sync at?
Bill Ince
CTSW (E-LSA)
Retired Heavy Equipment Operator

3Dreaming
Posts: 2777
Joined: Sun Jan 10, 2010 6:13 pm
Location: noble, IL USA

Re: Rotax 912 ULS loss of power in flight

Postby 3Dreaming » Mon Mar 23, 2020 9:22 am

I start with idle, but check as high as 4000 RPM. As long as they stay matched as RPM increases you should be good all the way to full throttle.

Wm.Ince
Posts: 965
Joined: Sun Nov 17, 2013 3:27 pm
Location: Clearwater, FL

Re: Rotax 912 ULS loss of power in flight

Postby Wm.Ince » Mon Mar 23, 2020 4:22 pm

3Dreaming wrote:I start with idle, but check as high as 4000 RPM. As long as they stay matched as RPM increases you should be good all the way to full throttle.

Okay, thanks a lot, 3Dreamer. . . :D
Bill Ince
CTSW (E-LSA)
Retired Heavy Equipment Operator

User avatar
bitten192
Posts: 97
Joined: Mon Dec 21, 2009 6:09 pm
Location: RICHLAND WA USA

Re: Rotax 912 ULS loss of power in flight

Postby bitten192 » Sun Mar 29, 2020 4:31 pm

Same thing happened to me two early springs in a row. After much trouble shooting the first time and replacement of throttle cables, fuel lines and cleaning carbs and fuel distribution block etc I finally dumped the fuel and and put in 100ll which corrected the problem. Second time (the next year) when I lost power I skipped the trouble shooting and just replaced the fuel. My theory is that gas station that supplies car gas was shifting from winter to summer blend and I had vapor lock. I now fly 100ll in the winter and 50/50 MOGAS/100ll rest of the year.

It was the gas.
Ernie
CFI, LSRM-A

Dave C
Posts: 32
Joined: Tue Jan 15, 2019 5:33 pm

Re: Rotax 912 ULS loss of power in flight

Postby Dave C » Wed Apr 01, 2020 12:08 pm

UPDATE:
I had a local LSRM meet me at the airport to take a look. He pulled the float bowls and there were some small specks of debris in both of them. They weren't large enough to show up in phone pictures. Debris plugging up one of the carbs seems to be the leading theory of the loss of power but because it cleared itself up immediately after landing there can be no obvious proof.

One thing that I didn't mention before was that this was the first flight after the annual was done and as part of that service all the fuel lines from the firewall forward were replaced. The new lines or the process of installing them could have introduced the debris.

User avatar
drseti
Posts: 6652
Joined: Sat Nov 28, 2009 6:42 pm
Location: Lock Haven PA
Contact:

Re: Rotax 912 ULS loss of power in flight

Postby drseti » Wed Apr 01, 2020 12:37 pm

Dave C wrote:The new lines or the process of installing them could have introduced the debris.


Very common. Especially when new fuel lines are installed over barbed fittings.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
Prof H Paul Shuch
PhD CFII DPE LSRM-A/GL/WS/PPC iRMT
AvSport LLC, KLHV
fly@AvSport.org
AvSport.org
facebook.com/SportFlying
SportPilotExaminer.US


Return to “Ask The Mechanic”

Who is online

Users browsing this forum: No registered users and 3 guests