ROTAX 912 - New style fuel pump/fuel pressure question

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.

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FastEddieB
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ROTAX 912 - New style fuel pump/fuel pressure question

Postby FastEddieB » Mon Apr 23, 2018 9:30 pm

Yesterday I FINALLY got around to replacing the original fuel pump on the ROTAX 912 in my 2007 Sky Arrow.

I had bought the pump some time ago, but fell into the "if it ain't broke..." mentality. But it was time to start on my second rubber parts replacement and I figured with the fuel lines it would make sense to do the new pump at the same time. Also installed the drain line as required.

I just finished with the fuel lines today, and have not done a runup yet. But something in the SB is just a tad unclear...

Image

My POH shows the acceptable fuel pressure range to be from 2.2 to 5.8 psi. Here's how my gauge is marked:

Image

In the latest ROTAX 912 Owners Manual I can find, it still says 2.2-5.8 psi, but then parenthetically says the high end is 7.26 psi "Applicable only for fuel pump from s/n 11.0036".

Am I correct in assuming that includes my new style fuel pump? I don't have the s/n here to check. If so, rather than try to remark the fuel pressure gauge, I'll just add a small placard with the new max psi.

Tomorrow when I do the runup I'll check the fuel pressure for any change and get the s/n of my pump.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
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ShawnM
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby ShawnM » Mon Apr 23, 2018 10:50 pm

Yes Eddie, although I’m not a mechanic if it’s the new Corona style pump then the high end is 7.2. My gauge range was easy to change since it’s Dynon glass. :mrgreen:

I was of the same mentality as you several years ago when the SB came out. I was reluctant to change it as my old pump was working beautifully but Rotax offered a free pump and I had to send my old one back. I figured, what the heck, it’s free.

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FastEddieB
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby FastEddieB » Tue Apr 24, 2018 8:10 am

Thanks! I’ll get to work on the placard.

As an off-topic aside, I thought it was quite a coincidence that this diagram came across my Twitter feed this morning:

Image

On the lower right, I discovered that “If it ain’t broke - don’t fix it” it actually has a name: Status Quo Bias!
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
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MrMorden
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby MrMorden » Tue Apr 24, 2018 11:14 am

I'm not convinced all cognitive bias is a bad thing. Some of them have developed as survival strategies, after all...
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2007 Flight Design CTSW E-LSA

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FastEddieB
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby FastEddieB » Tue Apr 24, 2018 11:41 am

MrMorden wrote:I'm not convinced all cognitive bias is a bad thing. Some of them have developed as survival strategies, after all...


Of course.

A rustling in the bushes was historically probably not a saber-toothed tiger.

But assuming that it wasn't could end up culling the gene pool for that tendency to assume. Whereas assuming it was a saber-toothed tiger when it wasn't had little downside.

Still, I think its generally good to be aware of these biases, along with other errors in reasoning, i.e. logical fallacies. Which are EVERYWHERE!

Unless that's a hasty generalization, of course! :wink:
Fast Eddie B.
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drseti
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby drseti » Tue Apr 24, 2018 11:47 am

FastEddieB wrote:
Unless that's a hasty generalization, of course! :wink:


Of course, all generalizations are untrue!
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
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MrMorden
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby MrMorden » Tue Apr 24, 2018 2:24 pm

I think the "if it ain't broke, don't fix it" can *sometimes* be valid. You are using your personal experience to color your decision of that of others to arrive at a decision. Of course, the "others" might have more info than you do, and you could always be a moment away from disaster, but all maintenance carries risks.

I agree that understanding bias is critical, even if you allow yourself to indulge in it occasionally! :) The key is to know why you are making decisions, and not to just let apathy make them for you
Andy Walker
Athens, GA
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2007 Flight Design CTSW E-LSA

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drseti
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby drseti » Tue Apr 24, 2018 2:37 pm

MrMorden wrote:I think the "if it ain't broke, don't fix it" can *sometimes* be valid.


I prefer the Mechanic's Corollary: if it ain't broke, break it. Then, fix it.
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
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FastEddieB
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby FastEddieB » Tue Apr 24, 2018 5:31 pm

I guess most ROTAX 912's already have the new style fuel pump in place, but here it is installed on mine:

Image

Fuel pressure solidly in the green:

Image

Finally, placarded the fuel pressure gauge with the new upper limit:

Image

Working on the logbook entry now, will test fly for return to service in the next couple of days.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
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FastEddieB@mac.com

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MrMorden
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby MrMorden » Tue Apr 24, 2018 8:06 pm

drseti wrote:
MrMorden wrote:I think the "if it ain't broke, don't fix it" can *sometimes* be valid.


I prefer the Mechanic's Corollary: if it ain't broke, break it. Then, fix it.


And don’t forget corollary 2: “If force doesn’t fix it, apply more of it.”
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA

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FastEddieB
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby FastEddieB » Tue Apr 24, 2018 8:27 pm

MrMorden wrote:
drseti wrote:
MrMorden wrote:I think the "if it ain't broke, don't fix it" can *sometimes* be valid.


I prefer the Mechanic's Corollary: if it ain't broke, break it. Then, fix it.


And don’t forget corollary 2: “If force doesn’t fix it, apply more of it.”


Or...get a bigger hammer! 8)
Fast Eddie B.
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Jim Hardin
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby Jim Hardin » Fri Apr 27, 2018 3:24 pm

So what was in the bushes :shock:

I didn't know the guy but do know the author who tells of a solder on point in VN. He heard a rustle in the bushes and it was indeed a tiger!
It lunged, clamped down on his head and commenced to drag him off. He managed a long burst and the tiger let him go...

How many have a tale like that to tell :wink:

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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby drseti » Fri Apr 27, 2018 4:08 pm

FastEddieB wrote:Or...get a bigger hammer! 8)


Is this what you had in mind, Eddie?

banjo_mute.jpg
banjo_mute.jpg (51.34 KiB) Viewed 1104 times
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

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FastEddieB
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby FastEddieB » Sat Apr 28, 2018 3:03 pm

Flew the plane today as a test flight.

Fuel pressures are definitely higher throughout. At the lower left, you can see it just touching the top of the old green, 6 psi, at what might be a normal cruise altitude and power setting.

Image

Bear in mind, more is not necessarily better. Same carbs on a motorcycle get enough fuel from just gravity feed, and too much can overpower the needle and seat. But even the new limit of 7.2 psi is not a whole lot of pressure.
Fast Eddie B.
Sky Arrow 600 E-LSA • N467SA
CFI, CFII, CFIME
FastEddieB@mac.com

3Dreaming
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Re: ROTAX 912 - New style fuel pump/fuel pressure question

Postby 3Dreaming » Sat Apr 28, 2018 4:24 pm

I had one airplane that the new fuel pump was to much for the carb. It would overpower the needle at idle and the engine would run rough. After trying a few things myself I removed the carb and sent it to Leading Edge Airfoils and they worked some magic on it and the problem went away.


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