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  #11  
Old 09-06-2011, 09:28 AM
prkaye prkaye is offline
 
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Quote:
RTV is the wrong thing to use anywhere around gasoline
Ok, good to know. Supposing that the nuts on those stainless steel hoses just won't tighten up enuogh to stop vapour from leaking through under the higher vapour pressure of auto gas, is there any *other* goupy product I can use to seal them up better? I may have some leftover Firewall 2000 I could use...
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  #12  
Old 09-06-2011, 10:09 AM
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RVbySDI RVbySDI is offline
 
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Quote:
Originally Posted by prkaye View Post
Ok, good to know. Supposing that the nuts on those stainless steel hoses just won't tighten up enuogh to stop vapour from leaking through under the higher vapour pressure of auto gas, is there any *other* goupy product I can use to seal them up better? I may have some leftover Firewall 2000 I could use...
As far as your troubleshooting goes, you might examine the flares on your tube fittings. It is possible you could have a bad flare that is allowing vapor to escape. The fix might involve re-flaring the fitting connections. Of course if your plane is like mine that would mean complete new tubing for sections where you would do this.
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  #13  
Old 09-06-2011, 10:20 AM
Phlyan Pan Phlyan Pan is offline
 
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Location: Rochester, NY
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If you plugged the vent and put some soapy water on the threads wouldn't that show you if they were in fact leaking? Of course, the tank would have to be under a slight amount of positive pressure I would think.
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  #14  
Old 09-06-2011, 10:23 AM
David-aviator David-aviator is offline
 
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Location: Chesterfield, Missouri
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Quote:
Originally Posted by prkaye View Post
Ok, good to know. Supposing that the nuts on those stainless steel hoses just won't tighten up enuogh to stop vapour from leaking through under the higher vapour pressure of auto gas, is there any *other* goupy product I can use to seal them up better? I may have some leftover Firewall 2000 I could use...
Phil,

All fuel has an odor. If its there, you have a leak. Whether it comes from mogas or 100LL is not relevant. Find the leak and fix it.

If your non standard vents lines and fittings are not up to the task replace them with what is recommended in the build plan.

No amount of glue or adhesive material is a proper fix for a leaking line or fitting.

Note. The vent system is open to atmospheric pressure, there is no such thing as a "high vapor pressure" causing a leak, that is total nonsense. It is possible you serviced the tank so full, fuel was flowing into the vent line at the filler cap and during taxi and in flight liquid fuel flowed out the vent exit, blew back and that's where you got the fuel fumes in the cabin. Turning final in slight slip or skid could cause this to occur then also. This phenomena has been reported before, I believe with the RV-8.
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Last edited by David-aviator : 09-06-2011 at 10:32 AM.
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  #15  
Old 09-06-2011, 10:24 AM
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John Clark John Clark is offline
 
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Phil, if the flare fittings are done properly and are secure, no "gooping" is going to change anything. If everything on your airplane is tight, you may be chasing a ghost. As Mark noted in post #5, fuel vented outside the airplane can cause an odor inside the cockpit. Our little aluminum airplanes are fairly "leaky" when it comes to air, plenty of lap joints and rivet lines to let a little air (and odor) in. With absolutely full tanks my '8' will have a slight smell of 100LL until the tanks are burned down a little. Fill it about an inch down, no smell.

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Last edited by John Clark : 09-06-2011 at 10:27 AM. Reason: Spelling
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  #16  
Old 09-06-2011, 10:25 AM
DEWATSON DEWATSON is offline
 
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Location: Quincy, Florida
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Default smell

I had a similar problem (RV8). The very top screw on the fuel indicator cover for the left fuel tank was seeping gasoline. They were installed properly with proseal, etc., so that was the last place I looked in search of the smell in the cockpit. I finally found it and gave the screw about 1/8 turn. It sealed up and the smell is gone. If you smell gasoline in the cockpit....FIND THE SOURCE!!!!!
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  #17  
Old 09-06-2011, 10:49 AM
prkaye prkaye is offline
 
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Yes, of course "find the source", as I indicated in my first post I have grounded the airplane until I sort this out.

Quote:
If your non standard vents lines and fittings are not up to the task replace them with what is recommended in the build plan.
All my lines, including the vent lines, are stainless flex lines from Bonaco. These are used on many RVs, and despite being "nonstandard", they are superior (and more expensive) than the rigid aluminum tubing lines recommended in the build plan. Therefore I doubt if the problem is incorrect flaring.

The fact that the smell really seems to come-up mainly at low power settings... is this a clue? Does this suggest it's the vent fittings?
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Last edited by prkaye : 09-06-2011 at 11:47 AM.
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  #18  
Old 09-06-2011, 11:54 AM
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erich weaver erich weaver is offline
 
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The fuel pumps only pressurize the fuel on their discharge end; there is suction on the entire length of fuel line connected to the input side of the pump. So, if there is a small leak anywhere on the input side, it will not necessarily result in visible leakage . I would second what was said in a previous post: SLIGHTLY pressurize each fuel tank to find any leaks in the system on the input side of the fuel pump. This will also pressurize the input lines where there is normally not any pressure, and force fuel to drip out from any leaks so that they are visible.

You can pressurize the fuel tanks by cutting out the valve from a bicycle innertube along with a small square of the surrounding tube and then taping it down over the tank fill hole. Pump air in by hand slowly, and monitor the pressure using water in clear tubing on the air vents to form a home-made manometer. Dont exceed several inches of water displacement in the tube to avoid over-pressurizing your tanks. When slightly pressurized, check for fuel smell and drips inside the cabin and at the wing root, wherever there are joints in the fuel lines.


erich
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  #19  
Old 09-06-2011, 01:43 PM
prkaye prkaye is offline
 
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But if it were an actual leak in the input fuel lines lines, it doesn't make sense (to me) that the odor would get much stronger when I'm throttled BACK at lower power settings. I notice it when I taxi, and then it goes away during cruise but when i throttle back while turning base or final I notice the smell strongly again. It seems to me if there were a leak on the input side, this would lead to an even stronger smell when more fuel is flowing at higher power. What I notice is the exact opposite.

Does anybody have a theory as to what could account for this behaviour? Not being an expert on this, it suggests to me maybe it is indeed somehow related to venting?
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  #20  
Old 09-06-2011, 02:50 PM
chaskuss chaskuss is offline
 
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Location: SE Florida
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Default Use Talc to find leaking fittings

Phil,
Forget the fancy electronic sniffer. Those things suck! Dust each of your fittings with Talc [talcum powder will work] If there is a leak, the Talc will be stained, even if the fuel all evaporates before you can inspect the fittings.
As others have already told you, goop will NOT fix the problem. The seal is made between the flare and the fitting. If you have a leak at a fitting, you must inspect the fitting for imperfections and correct the problem.
The only possible "short cut" fix would be to install special copper washers in the joint. See

https://www.pegasusautoracing.com/pr...p?product=3202

Actual cracking of the flare will require that the damaged area be cut off and re-flared. If the Talc test shows no signs of leaking, it's just the stinky Mogas and the vent system.
Charlie
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