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Old 11-06-2018, 07:50 PM
John C's Avatar
John C John C is offline
Join Date: Mar 2005
Location: Moundridge, KS
Posts: 149
Default Leaking fuel vent line in tailcone

I started smelling fuel during power back after takeoff or when I opened the canopy while taxiing on the ground. In flight, opening the heat vent or the side vents quickly cleared the smell. The usual sources, such as carberator bowl gasket or spitting fuel out the carburetor vent line were clean and dry.

Finally checked the fuel tank vent line aft of the bulkhead. Found where the fuel had been collecting. Notice the tightness of the small vent line. It had shrunk a substantial amount as slack in the line was gone.

At the top, the shrinkage had pulled the tee fitting down a substantial amount from near vertical and the flexible vent line easily pulled from the tee. The upper portion was hard and stiff. Overfilling the tank or taking off with a full tank would cause fuel to flow through the tee as it should. However, fuel would also flow into the third leg of the tee and leak into the aft portion of the fuselage.

It appears that the pressure change in the cockpit from pulling power after a climb or raising the canopy on the ground would pull the fumes from the tailcone and into the cockpit. Opening the vents while in flight would increase the cockpit pressure and keep the fumes in the tailcone.

The tube-within-a-tube was well seated. It appears that the fuel was flowing around the small plastic line (not pictured)

Instead of using plastic lines, I went to a 3/8 aluminum line. Bent it into a useful shape.

The upper end was easily installed. Make sure that the tubes are aligned with the tee.

I pulled the rivet for the plastic line and installed a snap bushing.

Works good now. You may want to check for shrinkage of the small line, and make sure that the tee is still pointed up so that the standpipe function is still effective. I have about 400 hours on the airplane and it has been in service about 2 1/2 years. Add a year or two for the initial installation of the vent lines.
John Clark
Moundridge, KS
RV-9A 90512 N6699 Sold
RV-12 120323 N6699Z 650 hours
dues paid 2021
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Old 11-07-2018, 01:21 PM
mike newall's Avatar
mike newall mike newall is offline
Join Date: Jan 2005
Location: Yorkshire, England
Posts: 2,196

Good spot.

We pre fuelled our 12 and smelled fuel the next day. Checked everywhere and of course........ It was the bulkhead fitting under the tunnel where the pushrods go

Backed it off, doused with Fuel Lube and re assembled - Pheeeew ! Worked.
"I add a little excitement, a little spice to your lives, and all you do is complain!" - Q

Donated in 2021
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Old 11-08-2018, 10:57 AM
EXflyer EXflyer is offline
Join Date: Jan 2016
Location: Chiloquin OR
Posts: 94
Default Plastic Line

I use those type of fittings with air line and the only type that will work is DOT brake line as it has an inner hard liner that does not collapse like that tubing does. I don not know if the DOT line is fuel proof or not. Also don't know about the fitting o rings being fuel proof. Have found that clear plastic lines do get hard when using fuel in them. The DOT line can be bought from any parts store that deals with semi trucks by the way.
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Old 11-08-2018, 12:30 PM
dwrichey's Avatar
dwrichey dwrichey is offline
Join Date: May 2009
Location: Reedley, California
Posts: 85

I would be concerned with the metal to metal contact between the two tubes, held together with tye-wraps. They will rub together, failure is only a matter of time.
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Old 11-08-2018, 05:32 PM
John C's Avatar
John C John C is offline
Join Date: Mar 2005
Location: Moundridge, KS
Posts: 149
Default Good point

I?ll fix it. John
John Clark
Moundridge, KS
RV-9A 90512 N6699 Sold
RV-12 120323 N6699Z 650 hours
dues paid 2021
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