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  #1  
Old 08-01-2019, 07:59 PM
Tacco Tacco is offline
 
Join Date: Jan 2017
Location: White Salmon, WA
Posts: 107
Default Fuel Smell in Cockpit

It’s happened twice. Once during the PAP while conducting the “time to climb” performance test, and once during the first flight I had a totally full fuel tank. I had read all the posts on probable causes and I went looking for the obvious. While removing the access panel to check the tank/fuel line tank fittings, I noticed, thanks to a liberal coating of exhaust products on the bottom of the airplane, that the tank had been venting significantly, at least during the second occurrence. As I followed the flow path aft, it was pretty clear the vented fuel was entering the fiberglass tall cone at the attachment. It does overlap the aluminum skin at this point. And btw, there was some traces of fuel on the trailing edge of the trim tabs. My conclusion was that it pooled in there then the fumes migrated forward through the tail cone to the cockpit.

I checked all the fittings and inspected the carbs anyway, but for those of you chasing sources of intermittent fuel fumes in the cockpit, you might want to consider this possibility as well as looking for a leak.
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  #2  
Old 08-01-2019, 11:38 PM
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Piper J3 Piper J3 is online now
 
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If you have the newer fuel tank vent fitting in the filler neck that could be cause of fuel dumping overboard when tank is full and nose-up climb. Best to not fill tank completely. Tank with fuel in filler neck will overflow even with plane stationary in the hanger - seen it several times.
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  #3  
Old 08-02-2019, 09:38 AM
Tacco Tacco is offline
 
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Yes I do and yes it is. Just never thought I’d smell it in the cockpit when it vents outside!
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  #4  
Old 08-02-2019, 04:09 PM
vic syracuse vic syracuse is offline
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More often than not when I smell fuel in the cockpit of the 12 in climb it can be traced back to the carb floats, so I would recommend checking those as well.

VIc
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  #5  
Old 08-02-2019, 05:25 PM
alexe alexe is offline
 
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+1 for what Vic said. Check your floats.
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  #6  
Old 08-02-2019, 09:04 PM
RFSchaller RFSchaller is offline
 
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Vic,

Just noticed your build history. Man you are a serial builder!😜

Rich
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  #7  
Old 08-03-2019, 08:00 AM
vic syracuse vic syracuse is offline
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Quote:
Originally Posted by RFSchaller View Post
Vic,

Just noticed your build history. Man you are a serial builder!😜

Rich
It kept me sane during all of those years in IT.

Vic
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  #8  
Old 08-03-2019, 08:52 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Make sure the tee for the anti-siphone line on the main vent line is pointed straight up. Even if the tank is really full, there should be no fuel dumping overboard in flight unless there is some major heating expansion going on.
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  #9  
Old 08-04-2019, 06:01 PM
Tacco Tacco is offline
 
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Location: White Salmon, WA
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Thanks Scott. The tee was horizontal. I twisted it vertical and put a dab of RTV on the plastic tube so to fix it to the the aluminum skin above the tee.

For the initial occurrence, here’s what I think happened: 3/4 full tank, high angle Vx climb from surface to 10k, fuel covered or sloshed over the vent connection, expanding air in tank void forced some fuel into the vent line then overboard. The air vent line, pointed downward at the tee just became part of the siphon path instead of performing an anti siphon function.

For the second occurrence, I think I had a sticky float. There was some residual (evaporated) fuel on the carb trays one carb. Not much but probably enough to smell. I pulled the bowl, floats weighed out fine. No debris in the bowl. Going to fly tomorrow so we’ll see.
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