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  #1  
Old 10-30-2022, 11:42 PM
glongpilot glongpilot is offline
 
Join Date: Dec 2012
Location: Johnston, IA
Posts: 25
Default Strong Fuel smell at cruise power

On my first flight 10-21-22 (912ULS carb. floats weigh fine) I smelled fuel slightly, not enough to be alarmed. I am burning 91 octane unleaded no ethanol mogas. I had my air vent open. On second flight last Friday I was testing roll issues and flew at 5150 RPM for several minutes. The fuel smell got really bad, so bad that I abandoned any more testing and returned to the airport. I did not have my air vent open due to cooler temps.

By the time I got to the ground the smell had almost dissipated. While taxiing to the hangar it was gone. I sat outside the hangar and ran the engine at about 4000 RPM for a minute, no smell. On shut down and opening the oil check door there was no smell coming from the engine and none in the cabin.

Any ideas? I have checked fuel lines and find no sign of leaks.
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Greg Long
RV-12 N719VA, 912ULS
First Flight Oct. 21, 2022
Builder's log www.gregsplane.com
glongpilot@gmail.com
VAF paid 2022
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  #2  
Old 10-31-2022, 01:00 AM
Ralph Inkster Ralph Inkster is offline
 
Join Date: Feb 2008
Location: Calgary, Alberta
Posts: 1,962
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I hope you ground the airplane till you find the fault…
Scary stuff!
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built a few RVs, rebuilt a few more, hot rodded more, & maintained/updated a big bunch more
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  #3  
Old 10-31-2022, 05:17 AM
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Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,820
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Look at drip pans under each carb for evidence of fuel. Also look at carb float bowl gasket - it may not be seated fully. Remove top cowling and run electric fuel pump to observe if fuel is overflowing carbs...

When you open canopy after plane is sitting for extended period (day)... do you smell fuel in the cabin?
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 830

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father - CFI) - USAAF 1st Lt. Captain B-17H
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  #4  
Old 10-31-2022, 07:12 AM
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gvouga gvouga is offline
 
Join Date: Aug 2005
Location: Raleigh, NC
Posts: 117
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Double check the security of the fuel lines between the wing tank and fuselage. If they are not fully tightened, the airflow will bring the smell into the cockpit during cruise flight. Ask me how I know...
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RV-7

Last edited by gvouga : 10-31-2022 at 07:20 AM.
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  #5  
Old 10-31-2022, 07:28 AM
sailvi767 sailvi767 is offline
 
Join Date: Sep 2010
Location: Charlotte NC
Posts: 1,503
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I think he is a RV12 that does not have wing tanks. I do agree on the other RV’s even a small leak can generate a lot of fumes. I spent some time trying to find a source of fumes only to find it was a hairline crack in a welded fitting.
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  #6  
Old 10-31-2022, 08:17 AM
JDAviator JDAviator is offline
 
Join Date: Oct 2006
Location: Land O Lakes, FL
Posts: 43
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When you do a power reduction, your fuel pump pressure increases. If you have a slight fuel seep anywhere on the pressure side of the fuel pump it is exacerbated at power reduction.

I had a similar issue to yours, but noticed it first in the pattern and on landing. By the time I taxiied to the hangar and shut down the smell was gone. Eventually I found numerous fuel "seeps" that became "leaks" with power reduction. This was not discovered until the airplane had flown several hours. The greatest leak was the outlet fitting on the gascolator, but it was seeping on both sides of the fuel flow transmitter, as well as the gascolator inlet fitting at the firewall. Once each of these fittings were retorqued, I've had no further issues.

**To be clear, I'm referring to the pipe fittings and not the B nuts on the flared fittings.
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RV-12
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Last edited by JDAviator : 10-31-2022 at 08:24 AM.
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  #7  
Old 10-31-2022, 08:34 AM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,820
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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….
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 830

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father - CFI) - USAAF 1st Lt. Captain B-17H
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  #8  
Old 10-31-2022, 09:57 AM
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Low Pass Low Pass is offline
 
Join Date: May 2006
Location: Texas
Posts: 2,195
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Suggest you strongly consider the grounding recommendation above until you know what you're dealing with. I had a leak recently that was moderately detectable in various phases of flight. I wrote it off several times to full tanks venting. (Which will sometimes result in a fuel smell in the cockpit.) Turned out to be a scary significant leak near the main pump...
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  #9  
Old 10-31-2022, 10:09 AM
DHeal DHeal is offline
 
Join Date: Sep 2006
Location: Windsor, California
Posts: 1,020
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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.
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David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B 2020) - N124DH flying since March 2014 - 1,200+ hours (as of Oct 2022)!
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  #10  
Old 10-31-2022, 11:31 AM
glongpilot glongpilot is offline
 
Join Date: Dec 2012
Location: Johnston, IA
Posts: 25
Default

Great suggestions - I have tried some already and will continue to look for sources. I'll report back on what i find.
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RV-12 N719VA, 912ULS
First Flight Oct. 21, 2022
Builder's log www.gregsplane.com
glongpilot@gmail.com
VAF paid 2022
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