fuel smell in cockpit

On take off and other times I'm getting gas smell. I feel that a little bit of fuel may be coming from the vent tubes on belly and is coming into the cockpit by way of the wing root. Tanks are not leaking, and the vent tubes about 1inch in length are cut for a positive pressure forward. Any ideas to help,rv4

I would check all your fuel line connections from the wing root, through the fuel selector and so forth all the way thru the firewall.
Look for tell tale blue staining.
Don

I had that faint fuel smell and found a loose nut on the bulkhead fitting under the wing to fuselage fairing. Don't forget the rear bulkhead rivets on your fuel tanks either. John

I occasionally get the same thing. I have inspected thoroughly all connections. They are all secure and no evidence of leaking. It only happens on take off with high angle of attack and with the aux electric pump on. I am interested in others thoughts.

Check your carb for staining ,as on my 4, with boost pump on the inline fuel pressure is at the high end for a carb, and can cause slight leakage . This may explain why it's at takeoff and high AOA. I turn my boost off as soon as I hit safe altitude. For the record, I have 2 electric Facet pumps and no mechanical. One runs continuous, and the other is boost.

I used to get fuel smell and it was from leaking around the seals where the fuel sender plates are screwed onto the tanks at the wing roots. Took plates off, got rid of old gaskets (think they may have been cork?), resealed with proseal, no more leaking or fuel smell.

Do you have the float or capacitor system in your tanks? I had a small weeping leak in the center of the connector (NCB ?) that was hard to fine, but pretty easy to fix with pro seal.

Vent line

I just did my annual, and found that the B-nut connecting my vent line inside the cockpit was not tight at all and blue marks on the floor, this explains why climbing to higher altitudes I always smelled fuel.

just something to check out for

Be sure to check around the fuel selecter. I once had a small leak underneath the lever.

Carb or fuel injected?

If you have a marvel carb.... lightly with finger tips try wiggling the bottom half of the body. After a few hundred hours of normal operation, the vibration can and will loosen the float bowl / bottom half of the carb body from the top half. Even if the screws have lock tabs and or lock wires, the threads loosen from vibration wear. It might not leak fuel on the ground but in flight they will, especially in a slip on approach. There is a SB or AD several years old on this. It is easy to check this one at every oil change when the cowl is off.

If injected, after shutdown, the fuel will heat and expand in the small lines that run to the injector bodies. The injectors have ports and fine screens that will vent the fuel & vapors under the cowl. If a shut down was just the right amount of time before start up and take off, and if your cockpit air is from the top side of the cowl, you can get a momentary fuel smell on the take off roll - but that is about the only time it would be noticed.

What F1R said

To elaborate, I have had the MA4SPA on my -4 loosen just as he noted. The aifilter snorkle intake on mine was rigged a bit too tight, and engine movement shook my bowl loose...but you will then also get some backfiring and idle issues that will follow as it sucks air. I re-worked my airbox with a bit more flex in the rubber seal to accomodate engine movement. No issues after that.

I just recently started smelling fuel right after landing. No evidence of leaks externally. I haven't pulled any access covers yet to look for loose fittings, but will re check all connections before its flown again. My vents are like the Rocket design, which are coiled in the wing root and exit out the bottom. I hope that's where it's coming from.

Fuel valves commonly have seals/O-rings that seep. May need to rebuild the valve. Or a fuel line is leaking. Rubber lines will eventually fail and aluminum lines can get hairline cracks.

stan albright said:

On take off and other times I'm getting gas smell. I feel that a little bit of fuel may be coming from the vent tubes on belly and is coming into the cockpit by way of the wing root. Tanks are not leaking, and the vent tubes about 1inch in length are cut for a positive pressure forward. Any ideas to help,rv4

Click to expand...

I had this problem on an old RV when the tanks where full. The very small venturi pressure was pulling the gas through. I know the fix is to grind the vent fittings so they face 45 degrees forward. This puts a mild positive pressure on them and remove the siphoning.

Stan---I think this is a common thing, although I dont know why. I fly quite a bit in Lee's Rocket, and we get the same thing. Not all the time, but its there. His system is bulletproof---so its a bit of a mystery.

Found it

After an extensive search I finally found out why I was smelling fuel. The hard line that goes down the tunnel has a cracked flare at the bulkhead fitting. We had to use a snake camera to find it. I'm glad We found the leak before it caused a catastrophic failure. My problem wasn't exactly what the OP was describing, but if all of a sudden you start smelling gas where you shouldn't, then it's time to "down" the plane and find the cause.