Carb line leaking fuel

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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Warmi
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Carb line leaking fuel

Postby Warmi » Sat Sep 22, 2018 8:05 pm

Recently noticed that I could smell fuel on takeoff ..

Testing it on the ground with the electric pump on we saw this ...
https://youtu.be/6lHAMTUFqXU

Is it a leaking carb or the fuel line ?
Last edited by Warmi on Sat Sep 22, 2018 8:29 pm, edited 1 time in total.
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Re: Carb line leaking fuel

Postby drseti » Sat Sep 22, 2018 8:24 pm

I tried to check the video, and YouTube said removed by the user.
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Re: Carb line leaking fuel

Postby Warmi » Sat Sep 22, 2018 8:29 pm

Sorry about that . I fixed it and recreated the link..
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Re: Carb line leaking fuel

Postby drseti » Sat Sep 22, 2018 8:41 pm

It looks like leakage at the banjo bolt attachment to the carb. Could be the hose, the fitting, or under-torquing of the hardware. If the hose is over 5 years old (regardless of flight hours) Rotax calls for replacing it, along with all other engine rubber. If it's less than 5, the hose is probably OK unless the fitting has been removed and replaced (that can damage the rubber). But have a mechanic check the torque of that banjo bolt. In any case, it's unlikely to be the carb itself. When they leak, it's typically around the float bowl gasket, not at the hose fitting. And do NOT fly the plane or even start the engine until this has been resolved!
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
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AvSport.org
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Re: Carb line leaking fuel

Postby Warmi » Sat Sep 22, 2018 8:46 pm

I had 5 year rubber replacement done about 10 months ago so probably some kind of delayed side effect of that ... I will ask the guy who did the 5 year come over to the hangar to check it out on Monday.

Thanks
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Re: Carb line leaking fuel

Postby ShawnM » Sat Sep 22, 2018 10:37 pm

Could be the ear clamp or hose clamp that was used as well. Since we can’t see under the fire sleeve it’ll be hard to guess. Seems like it’s leaking from a weak clamp and filling the fire sleeve.

Could also be a lose banjo bolt as Paul stated and leaking into the fire sleeve.

Do you have the new silicone hoses or did you use a standard rubber hose? If rubber I hope whoever did your hose change used the ear clamps or a smooth band screw clamp. Never use a standard hose clamp with the serrated band. Those clamps are the worst for aviation and should never be used as they cause leaks by themselves. Only ear clamps or smooth band clamps.

Please report back as to what you find on Monday. And as Paul said, don’t start it.

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Re: Carb line leaking fuel

Postby Warmi » Sun Sep 23, 2018 4:55 am

Thanks for your input guys.

The 5 year job was done at this place http://www.theultralightplace.com
I am confident it was done acoording to the best practices , Jim Leon has been working with a Rotax engines since late 90s and is a go-to guy for Rotax service around Chicago area.

The funny thing is that just last week I did my first carb balancing and at first I thought maybe I messed up something with the carbs and it was overflowing or something ... but there is nothing really to mess up there and after the balancing the engine ran and still runs very smooth and the only sign was the fuel smell - will see ...
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Re: Carb line leaking fuel

Postby roger lee » Sun Sep 23, 2018 8:38 am

It does look like it's coming from the Banjo bolt area. There are three crush washers for that fitting. Many either drop one or put two on top of each other. I would take the Banjo bolt out and check the crush washers. It could also be that it just needs tightening. If these are the cause then the clamp that holds the hose on would be suspect.
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Re: Carb line leaking fuel

Postby 3Dreaming » Wed Sep 26, 2018 8:39 am

So what did you find?

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Re: Carb line leaking fuel

Postby MrMorden » Wed Sep 26, 2018 9:07 am

Squeezing the hose causes a large leak, I'm guessing it's the hose, either from a too-loose clamp, the hose not fully seated on the banjo fitting, or a hose integrity issue (hole/split/tear). It's also possible the clamp is too far down on the hose and not clamping around the fitting.

That's scary, it's a quite a bit of fuel leaking. Make sure you check both sides very carefully, and I'd take a look at every other hose I could put my eyes on as well.
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Re: Carb line leaking fuel

Postby Warmi » Wed Sep 26, 2018 9:13 am

The mechanic was unable to come on Monday but after looking at it more closely ( pushed back the fire sleeve etc) ,looks like the leak originates at the banjo bolt area - I blocked off the hose and I was still getting a myst like distribution coming directly from the banjo bolt area - I ordered a set of crush washers and will open it up and try to diagnose it further later this weeks.
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Re: Carb line leaking fuel

Postby 3Dreaming » Wed Sep 26, 2018 4:00 pm

The gaskets are a 950-141, and the bolt torque is 90 inch pounds.

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Re: Carb line leaking fuel

Postby Warmi » Wed Sep 26, 2018 7:31 pm

3Dreaming wrote:The gaskets are a 950-141, and the bolt torque is 90 inch pounds.


Thanks do you know which clamp would be suitable for the carb fuel hose ? I see like dozen clamp sizes at the Leading Edge store :D

https://www.leadingedgeairfoils.com/cat ... Fuel+clamp
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Re: Carb line leaking fuel

Postby drseti » Wed Sep 26, 2018 8:04 pm

Warmi wrote:do you know which clamp would be suitable for the carb fuel hose ?


I've always been partial to the Oetiker clamps. Sometimes called "stainless steel ear clamps":

https://www.leadingedgeairfoils.com/stainless-ear-clamp-15-32-to-37-64.html
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

Warmi
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Re: Carb line leaking fuel

Postby Warmi » Wed Sep 26, 2018 8:40 pm

Got it. Thanks
Flying Sting S4 ( N184WA ) out of Illinois


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