Champ Mystery fuel smell in my L-16/7BCM...

[Low Lead]

I'm chasing a strong fuel smell in my 7BCM - I never see the fuel but I smell it in flight when my nose tank is full. This aircraft has the original 13 gallon nose tank and a 5 gallon wing tank which I have emptied and closed the valve to in order to eliminate one source. I get a strong fuel odor when my nose tank is above 1/2 full. There is no loss of fuel when parked and no streaking of fuel anywhere under the panel. So far here is what I've done:

- Emptied and bore scoped the nose tank and detected no internal cracks.
- Rebuilt the gascolator with new seals and a new test valve.
- Replaced the seal in the nose tank fuel cap.
- Sealed any firewall holes with fresh RTV.

No dice. The primer is dry and all of the fuel valves are recent Burl's. Can anyone think of any next steps? Pressure test the nose tank? Pull the panel and the tank and send it out for mag-pen testing? Get new wings with dual tanks and lose the nose tank? (Kidding about the new wings.)

 

[Bob Turner]

Most wing tank valves are above the top of the main fuel tank. Check those lines and fittings before doing anything rash. Might even disconnect and plug the inlet to make sure. I can picture a pinhole in the line at about the half fuel level.

 

[Tangogawd]

Inspect the entire length of fuel tubing. I have found several over the years where corrosion or damage/ pinching of the tubing caused leaks through the tube wall. Check all fittings for clean connections, and the flaring and an fittings where they mate for cleanliness, burrs, and cracks. Maybe head pressure from 1/2+ fuel is forcing it out of some small imperfection.

Inspect around the filler neck base of the tank for cracks. Very common to form cracks there, especially when folks hang the fuel nozzle or gas can on it.

I dont know the champ fuel system, so just guessing

 

[Low Lead]

Excellent advice - thanks gentlemen - my leak hunt continues. I think the biggest clue is the 1/2 tank factor. I've taken to keeping it at/below 1/2 tank and refilling it to 1/2 from my wing tank but that will get old soon.