What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Smell raw Gas fumes

Bill Phillips

Well Known Member
on take off if I pull up sharp on take off and do a max climb I get a good wiff of raw gas in the cockpit for maybe 8-10 seconds. Does it with full or 1/4 full tanks, elec fuel pump on or off, either tank on line. I've checked everywhere for a stain, can't find any. Is it possible the gas is venting out the bottom vent lines and I'm getting a wiff from that? No smell on a normal takeoff or climb (600-1200 fpm). Never smelled any gas in loops or rolls. So ? anybody experienced this before?
Bill of Georgia RV-8A Bluebird, 100 hrs
 
Fuel smell

Bill, take the cowl off and remove the airbox, pressurize the system while watching for leaks.
 
on take off if I pull up sharp on take off and do a max climb I get a good wiff of raw gas in the cockpit for maybe 8-10 seconds. Does it with full or 1/4 full tanks, elec fuel pump on or off, either tank on line. I've checked everywhere for a stain, can't find any. Is it possible the gas is venting out the bottom vent lines and I'm getting a wiff from that? No smell on a normal takeoff or climb (600-1200 fpm). Never smelled any gas in loops or rolls. So ? anybody experienced this before?
Bill of Georgia RV-8A Bluebird, 100 hrs

Check your fuel lines that go from the wing tanks to the fuselage. I had a loose nut on the tank where the Al line connects during my phase 1 testing. I would smell fuel in a climb just like you are describing. I eventually found some blue staining on the belly where the wing root fairings end. I know you mentioned no staining, but it took about 20hrs before I could see a noticeable stain.
 
check your vent lines too

I found a loose nut on one of my vent lines under some insulation (inside cabin) that was causing intermittent fuel smells on climbout. Spent lots of time looking for the source before I found it.
 
Full tanks and steady, steep climb - yes, you will push some gas out the vents. If the deck angle is steep, but steady, fuel will cover the vent tubes in the tanks. The increasing altitude will generate a pressure difference inside the tanks, and the vent will be doing exactly what it is supposed to do - vent. Only fuel will come out. Quite normal for full tanks. Can't explain why you are getting it with 1/4 tanks. You could try extending the vents temporarily much further below the belly and see if it goes away.
 
If your vent lines are routed up high in the cockpit and then back down as per plans take a mirror and look very carefully in the location near the bottom of the vent lines near the rudder cable and see if the rudder cable has worn a hole in the vent lines. After months of work trying to find a problem in the first RV-6A I bought I discovered such problem, repaired the vent line, installed a protective cover over the vent line where the rudder cable had been rubbing and solved the problem.
 
I chased that problem for 20 hrs ...

.... Finally pulled the wing root fairings and found one screw holding the float plate/cover was leaking. Not enough of a drip to cause a stain visible from the bottom, but just enough you could smell it on a regular basis. The leak was barely enough to leave a blue stain on e float cover. I drained the tank, removed the screw, goobered it with aviation Permatex, and replaced. That fixed it.
 
Geart Replies

I appreciate the responses. A hanger bum buddy mentioned the overflow tube from the mec fuel pump. Anybody got an idea whether a steep climb can cause a flushing of fuel there? The Bluebird is not fuel injected, just one really big carb. Bill
 
carb vent ?

I'm not an expert on carburetors but don't they have float chamber vents that might spill a little fuel in a steep climb?.
My plane has fuel injection so I'm just guessing about this.
 
Broken vent tube

I had a broken fuel tank vent line in my RV4 - at the top where it makes a 180 degree turn back down....Yikes!!!
 
My experience with fuel smell in the cockpit was from a leaking Andair fuel valve. Apparently they had a batch with bad o-rings, this was around three years ago. They sent a new one and we've been flying stink free for several hundred hours now.
 
RV4 vent

The vent tube was broken completely in two - I do not know what caused this - maybe over stressed when built. Just happy I found it....
Skipper RV7
 
gas fumes

Your gas smell is probably coming from a crack in the tubing between the firewall and the manifold pressure gauge. I had the same problem and it only happens at full power when manifold pressure reads higher than ambient pressure.
 
I had the exact same thing on my RV-7A. Vents were plumbed per the plans, and I would always smell gas after leveling off after a climb with full or close to full tanks.

It turned out the interior flare nut on the fitting for the vent line for one of the tanks was loose where it penetrated the floor - right at the exit of the vent so to speak. Apparently in the climb attitude with full tanks some gas got into the vent line and after leveling off a small amount was pushed out of the vent. With the nut loose a bit of this ended up in the cockpit. I did not notice any blue stains but the smell went away after I properly torqued the nut.

I would think a loose fitting/crack anywhere in the vent line inside the cabin could result in the same issue.
 
Thanks

for all the good input. I'm reinspecting ever line and connection. I'll start first with the vent line and work my way through all the possibilities. Good flying to you all, Bill RV-8A "Bluebird" 100 hrs
 
RE-Fuel Leak

I had a fuel leak that I smelled for about a month before I could find it. The gas was sqeezing through the threads of a fitting, but not enough to drip. It would evaporate and I could smell it but no stains anywhere. I found it by smelling each fitting. If the fitting is in a tight spot use a small rubber hose and place next to the fitting and of course sniff the other end and the smell will come to you if there is any leak at that joint.
 
Back
Top