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Old 10-31-2022, 12:15 PM
NinerBikes NinerBikes is offline
Join Date: Dec 2018
Location: Granada Hills
Posts: 1,302

Also check the screws and gasket of your fuel meter sending gauge on your fuel tank. They shouldn't but they can come loose.
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Old 10-31-2022, 01:54 PM
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Piper J3 Piper J3 is offline
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,820

About a month ago… a friend’s Synergy-built RV-12 (5 years old) developed a leak at top edge of the large front fuel level sender plate. We removed the plate to discover bright shiny Alclad Aluminum surfaces that were never scuffed-up. Sealant was very thin and peeled off in sheets – required very little mechanical scrapping. My guess is sealant was not mixed at correct ratio. Used Pro-Seal at 10:1 and applied correct thickness. Now we’re doing the waiting game on seams and rivet heads…
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Old 10-31-2022, 02:05 PM
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greghughespdx greghughespdx is offline
Join Date: Nov 2011
Location: Aurora, OR
Posts: 1,260

Originally Posted by DHeal View Post
Typical RV-12 ULS fuel smell sources include:

-- Overweight/sinking carb floats
-- Improperly seated/broken carb bowl gaskets or float locating pins
-- Loose/leaking fuel lines/connections -- both firewall forward and through the
fuselage (tank, electric pump, selector valve, gascolator, etc.)
-- Properly balanced carbs (to minimize engine vibration)
-- Fuel pump pressures within spec

Good suggestions from above responders. Be sure to check all fuel components for leaks with the cowls off and the fuel system pressurized by the electric fuel pump.
Originally Posted by Piper J3 View Post
I have used a UV tracer ACDelco 1148963 Fluorescent Leak Detection Dye to find small leak in my RV-12 fuel tank. Mix tracer with fuel, go fly, and then use a bright UV flashlight to highlight the leak. Works a charm….
Good advice above. If you have not already pulled the cockpit covers to the tunnel through which the fuel lines run and checked the pump and fittings there under pressure, I would do so before further flight for sure. And, as people have already suggested a couple of times, be sure to find and address the source of the issue before flying again.
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Old 11-01-2022, 09:40 AM
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frankd frankd is offline
Join Date: Apr 2006
Location: Ponte Vedra FL & Point Pleasant Beach NJ
Posts: 431
Default Fuel Line flairs

I had this issue with my 12 a couple of years ago. We finally tracked it down to a faulty flair on one if the fuel lines/tubes. That is likely worth a look.
Frank Dombroski
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Old 11-01-2022, 10:59 AM
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jrtens jrtens is offline
Join Date: Apr 2018
Location: Seattle
Posts: 289

Originally Posted by Piper J3 View Post
I have used a UV tracer ACDelco 1148963 Fluorescent Leak Detection Dye to find small leak in my RV-12 fuel tank. Mix tracer with fuel, go fly, and then use a bright UV flashlight to highlight the leak. Works a charm….
If you don't do this you could at least fill up with 100LL. The blue dye should help locate a leak.
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Old 11-01-2022, 12:01 PM
seagull seagull is offline
Join Date: Dec 2019
Location: Highland, CA
Posts: 537

This may not relevant to the newer model, mine is a 2015 ULS. There is a vent line to the rear of the fuel tank bulkhead. Mine had come loose and was venting into the tail cone. When connected properly the vent exists out the bottom of the fuselage.

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Old 11-02-2022, 07:51 PM
DaveWelch DaveWelch is offline
Join Date: Mar 2005
Location: Keystone Heights, FL
Posts: 504

As Greg said, you've gotten a LOT of good advice and suggestions where to look.
I had several leaks after first couple of flights. That's why they call them tests.
One thing I haven't seen mentioned is sealants.
Be sure to use the current Van's recommended sealants at each location.
Based on my experience from an early 12 kit, I would NOT use Permatex #2 nor "Fuel Seal" in any location. I spent many hours cleaning and resealing fuel and brake line connections after first using them. As I recall they were recommended at the time years ago.
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Old 11-22-2022, 10:29 PM
glongpilot glongpilot is offline
Join Date: Dec 2012
Location: Johnston, IA
Posts: 25
Smile Fuel smell fixed

Thanks for all of the suggestions. I spent time and checked all the fuel lines and fittings from start to finish and found no leaks. I checked the carburetor bowls gaskets, no problem. The only things I "fixed" was I tightened the fuel filler neck rubber hose clamps. They were pretty tight but I was able to crank them down even more. Plus I made sure the filler neck flange to the turtle deck was well sealed. That should not have been an issue because if the fuel cap is tight then no fumes should come out though there.

I suspect fuel fumes were coming out of the tank at the filler neck fitting during high RPM and air speed. Maybe some kind of pressure differential caused it.

Anyway, I have flown twice since then and have no fuel smell.
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Old 11-23-2022, 04:50 AM
F1R F1R is offline
Join Date: Nov 2010
Location: ____
Posts: 944
Default One more look

On AC with a header tank or any tank that is above the fuel selector valve, there is static pressure present at the valve any time the tapered core stopc0ck is un seated to rotate to the next position. There is a tiny volume of gas that can find it's way to drain into the cockpit around the selector shaft. No leaks will be evident when the selector is stationary. Only right after rotating the selector shaft will there be evidence of fuel escaping for a few seconds. A new O-ring with a touch of DC4 or grease or lube, will normally fix the issue.

There are a lot of selector valve designs , but at least a few of them behave as described above if the o ring is old, dry & cracked.

Last edited by F1R : 11-23-2022 at 04:54 AM.
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Old 11-23-2022, 01:35 PM
bobg56 bobg56 is offline
Join Date: Nov 2018
Location: Peachtree City, GA
Posts: 272

Something else to look at is the bottom of the float bowls, early model float bowls have the float guide pins going all the way through the bowl. I had one come loose and exposed a 3/32 hole which dumped a lot of fuel onto the drip pan. The newer version bowls don't have the pin hole going all the way through...if you have the old style I would at the very least epoxy over the holes. You can order the newer bowls from Lockwood...the previous design was not good, I had fuel running out my cowl when I shut down.
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