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  #31  
Old 09-06-2011, 09:40 PM
Mark Burns's Avatar
Mark Burns Mark Burns is offline
 
Join Date: Jan 2005
Location: Ruston, Louisiana
Posts: 879
Default Exhaust

I think what you are smelling is just unburned fuel coming out the exhaust.
At low power settings it's running rich and just finding it's way into the cabin.
Try really leaning it at that low power setting and see if it helps.

Mark
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Ruston, Louisiana
RV-7A N781CM 1,650+ hrs
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  #32  
Old 09-06-2011, 10:06 PM
nucleus nucleus is offline
 
Join Date: Sep 2006
Location: Bozeman, Montana
Posts: 858
Lightbulb My Fuel Smell in the Cockpit Experience

Two or three times now I have smell gas fumes in the cockpit, always in cruise with no preceding changes. I have looked at every single cockpit fuel connection with mirrors and magnifying glasses, not a spot of blue anywhere.

Based on my experience I believe it is a vent issue. Reinforcing this theory, it has only happened on hot days. Worth checking every single connection very carefully before you reach this conclusion, however.

I also have a very sensitive schnoz.

Hans
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  #33  
Old 09-06-2011, 10:19 PM
erich weaver's Avatar
erich weaver erich weaver is offline
 
Join Date: Aug 2006
Location: santa barbara, CA
Posts: 1,682
Default

Do you get the odor in the cockpit at idle either without moving or during taxi? If so, why not do an experiment and hook up some tubing over the tank vents and run it back to the tail, secured with tape, away from the cabin. then sit at idle and during taxi and see if you still get the odor. No smell would confirm that it is the vents. I'm thinking it's not, but can't rule it out either. Might be worth a try.

Erich
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  #34  
Old 09-07-2011, 07:28 AM
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jthocker jthocker is offline
 
Join Date: Jan 2005
Location: Cincinnati, Ohio
Posts: 1,060
Default

Phil,
I can't see on your profile but I'm guessing you might have an O-320 in your RV9A. If it's carbed, you might have a leak in your accelerator pump.
I had this happen on my RV4 many years ago. I would get a strong fuel smell when I throttled back. I only found the leak when I switched to 80 octane. That stuff left visible stains on the firewall and carb area. It was a simple fix, for the old carb I was using. I got an accelerator pump kit, installed it, no more stains, no more smell! Good luck!
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  #35  
Old 09-07-2011, 08:11 AM
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F1Boss F1Boss is offline
 
Join Date: Aug 2006
Location: Taylor Texas
Posts: 811
Default Never thought of that!

Quote:
Originally Posted by jthocker View Post
Phil,
I can't see on your profile but I'm guessing you might have an O-320 in your RV9A. If it's carbed, you might have a leak in your accelerator pump.
I had this happen on my RV4 many years ago. I would get a strong fuel smell when I throttled back. I only found the leak when I switched to 80 octane. That stuff left visible stains on the firewall and carb area. It was a simple fix, for the old carb I was using. I got an accelerator pump kit, installed it, no more stains, no more smell! Good luck!
Good advice, Mutha.

FWIW, I run MOGAS on occasion in the 550. I get a smell in the cockpit too - but never with 100LL. My suggestion is that there are no leaks; you are smelling vapors - probably coming in thru the flap actuator holes (directly behind the vents - not the best plan) - it could be simply that you (and the rest of us) are used to the 100LL smell, and don't smell it anymore. Ex: I worked in a dairy for a few years (previous life), and I didn't smell anything, but visitors sure did!

I will volunteer that if you don't see any obvious stains, blue or otherwise, you are good to go. Please do check for leaks, tho!

Carry on!
Mark
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  #36  
Old 09-07-2011, 08:20 AM
prkaye prkaye is offline
 
Join Date: Jun 2006
Location: Ottawa, Ontario, Canada
Posts: 2,116
Default

Ok, thanks guys. This gives me lots of things to look for.
Indeed I had wondered whether the smell was coming from the exhaust getting in through either the gear-leg penetration holes or the flap actuator holes. I'll seal both of those up too.

I do have a carb'd O-320. Is the "accelerator pump" the same thing as the cylindrical mechanical fuel pump mounted at the back of my engine? I'll definately check that for leaks...any possibility fuel leak FWF is quite a scary thought to me.

I'm going to plan to spend a day out at the hangar checking all this stuff before I fly again.
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Last edited by prkaye : 09-07-2011 at 08:29 AM.
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  #37  
Old 09-07-2011, 09:30 AM
chaskuss chaskuss is offline
 
Join Date: Mar 2005
Location: SE Florida
Posts: 1,499
Default Don't confuse the fuel pump with the accelerator pump

Quote:
Originally Posted by prkaye View Post
snipped Is the "accelerator pump" the same thing as the cylindrical mechanical fuel pump mounted at the back of my engine? snipped.
Phil,
NO, the accelerator pump is part of your carburetor. Look carefully at your carb. You will see a round shaft coming out of the body of the carb. There is a seal between that shaft [accelerator pump shaft] and the carb body. This is where a leak could develop.
FYI, I have a video on rebuilding these carbs. Contact me via email [click on my user name, at the top of this post to get that info] if you would like a copy of it.
Charlie
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  #38  
Old 09-15-2011, 09:12 AM
prkaye prkaye is offline
 
Join Date: Jun 2006
Location: Ottawa, Ontario, Canada
Posts: 2,116
Default leak found

So I spent some time yesterday tracking this down.
With the engine off, I started the boost pump and fairly quickly got a whiff of gas. So I started checking fittings.
I found a leak through the pipe-thread on the elbow fitting that penetrates the firewall into the gascolator. Gas seeped out through the tapered pipe thread when the fuel pump was on (this is the first fitting downstream of the fuel pump, so probably a fair bit of pressure there). I could actually tell that the carpet underneath that fitting had been getting gas on it.
I replaced the elbow and put Loctite 567 Thread Sealant on the threads this time (i had previously just used fuel lube). Waiting a couple of days for the sealant to cure and then I'll pressurize the system and check again.
I HATE TAPERED PIPE THREADS!!!
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  #39  
Old 09-15-2011, 09:17 AM
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Mike S Mike S is offline
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
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Default

Quote:
Originally Posted by prkaye View Post
I found a leak through the pipe-thread on the elbow fitting that penetrates the firewall into the gascolator.
Kinda nice when you find, and fix the things that can kill you
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Flying as of 12/4/2010

Phase 1 done, 2/4/2011

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  #40  
Old 10-11-2011, 06:43 AM
prkaye prkaye is offline
 
Join Date: Jun 2006
Location: Ottawa, Ontario, Canada
Posts: 2,116
Default bit of smell in climb now

Ok, well after replacing and sealing that fitting (and sealing my flap rod egress holes) i thought i had the smell gone. Almost. The other day I filled up with V-Power again, and again noticed a smell. I double checked that fitting, which has remained dry.
This time the smell was much less potent (only whiffs really), and after a few hours of flying and experimenting, it seems I only get whiffs of it in a climb. At cruise, no smell - even a high power cruise. This suggests to me that it's aircraft attitude / AOA that determines when I get the whiffs of fuel smell (and only noticeable with auto gas - great way to test!). Does this suggest it is indeed a venting problem at this point? It's hard to diagnose a leaky vent fitting, since there's normally no fluid in it -but I'll unscrew and visually check the nuts and flares anyway.
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