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fuel smell suggestions

seagull

Well Known Member
I just finished my conditional inspection. I did not find any issues that would relate to this problem.

When I land, taxi off the runway, then pop the canopy I smell fuel. I do not ever smell it in flight. After I taxi back to my hangar and get out, approximately 3 minutes, the smell is gone. I open the oil door and there is no smell. I have removed the top cowl and checked for stains in the carb trays, nothing. I know I will eventually find the source but was hoping for some direction or someone else with the same experience.
 
He mentions carb trays, so 912ULS. Examine the clear float bowl overflow tubes. Are they still clear or yellowish/brown? Also are tubes threaded thru the float retaining bale wires correctly? Did you remove fuel tank during inspection?
 
Fuel smell

I finally found that I had a weep somewhere in the lines that attached to the fuel shut off valve or after the valve and the line going the fire wall. Stain of fuel on floor under the tunnel or seat pan fuel valve. So open that area and look.

Hope this helps.
 
Yes, 912ULS

The overflow tubes are yellowish brown. They are trapped between the float bowl and the bail wire. If fuel was to come out of the overflow it would drip into the tray and leave a stain.

During the inspection I had the tunnel completely open and removed the tank to look for a small leak that had left a stain on the bottom sheet metal. The leak was (2) of the screws that attach the large ring on the float, (front of tank). These are visible behind the passenger seat, they were removed and sealed with 3M 567. That leak has not reappeared.

Keep in mind I only smell it after landing and lifting the canopy a few inches, then it stops. The plane is hangared with the canopy closed and fuel in the tank. When I open the hangar the next day there is no smell, and when I open the canopy there is no smell.

Thanks for the ideas, keep them coming.
 
Where is the fuel tank vent located? Is a hole drilled in fuel tank cap?
If so, the smell could be coming from that vent.
 
Yes, 912ULS

The overflow tubes are yellowish brown. They are trapped between the float bowl and the bail wire. If fuel was to come out of the overflow it would drip into the tray and leave a stain.

During the inspection I had the tunnel completely open and removed the tank to look for a small leak that had left a stain on the bottom sheet metal. The leak was (2) of the screws that attach the large ring on the float, (front of tank). These are visible behind the passenger seat, they were removed and sealed with 3M 567. That leak has not reappeared.

Keep in mind I only smell it after landing and lifting the canopy a few inches, then it stops. The plane is hangared with the canopy closed and fuel in the tank. When I open the hangar the next day there is no smell, and when I open the canopy there is no smell.

Thanks for the ideas, keep them coming.

This description makes it sound related to the carburetors.

I may have missed it but have you measured the weights of of the carb. floats?
 
You say there were no stains in the drip trays but look carefully. Really hard to see if its a small amount. Clean the trays up and take a dry-erase marker and "color" up the area near the drip tube. If you smell gas again, check the trays - should be real easy to see the where the gas has washed away the dry-erase ink. If you do see fuel leakage in the trays, check the floats.
 
I had leaking bowl gaskets on my carbs and had to replace them, but I did see leakage on the drip trays. Have you considered adding a compatible dye to your fuel or using blue AVGAS to make a stain more identifiable?
 
I did weigh the floats a while back after going through some bad ones. The current ones weighed good but that was 3 months ago, I will check them again.

I like the idea of the dry erase, I will do that also.
 
I used fluorescent leak detection dye to find a stubborn leak in my fuel tank. The fluorescent tracer will show smallest leak.

Worked a charm?




 
Seagull-

Three quick checks of the carbs ...
1. verify the weight of the floats are OK
2. verify there is no crud under the needle valves attached to the float arm
3. verify the float arms are adjusted properly so the level of the fuel in the bowl is not too high.

Now that we are in the season of warmer weather, make sure you are NOT using a winter blend auto fuel. Another thought is to see if you get the aforementioned fuel smell when running 100LL.

If all of the above checks out, don't overlook checking the drain line from the mechanical fuel pump. The mechanical fuel pump could be weeping fuel while the engine is running (not good) so you may be smelling that ... but with the engine shut off, there would no longer be fuel weeping from the pump. Suppose placing some Styrofoam under the drain tubing would give an indication if that line was leaking because the fuel will melt the Styrofoam giving you a visual indication.

Happy flying,
 
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I have the fluorescent dye coming, thanks Jim. After running that through the system I'll pull the top cowl. Based on what / where I see I will recheck the float weights and check the adjustment on the float arms.

I'll report back my findings.
 
I just finished my CI and found a very small weep coming from the Fuel Flow Transducer. I pulled out the sensor and removed the fittings, cleaned them up and used thread sealant to reinstall them. Then reinstalled the transducer. To check if it still leaked I put a small piece of white paper under it and ran the fuel pump, then test ran the engine and found no sign of further leaks.

The fuel valve is in the same area so a piece of paper down there can tell you a lot. You will see right away if there are any leaks.
 
I put the dye in the tank and went out and flew .5, came back, pulled the cowl and saw some coloring around the carbs. Without comparison, and having never used the dye before I wasn't sure if it was old or new. In hindsight I think it may have been old fuel, it was more orange than yellow.

I ran the pump for .5 minutes and removed both carburetor bowls. The fuel levels were about .52" from the top on both with the floats removed. The float weights were 3.30 grams for both rights and 3.15 and 3.20 grams on the left. The gaskets on both carbs both looked good but I replaced them just to be sure. I used part #15-08666 gaskets.

After reassembly I ran the fuel pump for .5 minutes. I rechecked my work with the black light and when I shook the carbs slightly I could see the fuel seeping out of the gasket on both bowls. I disassembled the left carb bowl and carefully re-seated the gasket, refilled the carb and with a little sloshing could see the fuel seep under the gasket again. This dye stuff works real good for seeing the leaks.

Why with new gaskets is the bowl leaking?
Does it take some time for the gasket to seat?
Should I use different gaskets?
 
I have used those 15-0866 gaskets (the turquiose-colored ones) without any issues since my engine was new 900+hours ago. The original OEM thin cork gaskets that the engine was delivered with did not impress me. Have you checked on the Rotax-Owner site (https://www.rotax-owner.com/en/general-tech-discussion?view=search) -- Search: BOWL for possible remedies. I usually lightly rub the new gasket with a thin coating of oil prior to use. I would be reluctant to use any significant sealant. Are your bowl sealing surfaces flat and clean?
 
For what?s worth

My experience was I purchased some after market rubber type gasket that were cheaper than what Lockwood sold the cardboard type gaskets. I?m not sure if these were Vitron.

I had some leaking issues, inconsist, holding most of the time but leaking others. A Rotax specialist felt I should go back to the Rotax OEM cardboard type gaskets and no issues since.

However I did the 400 hr engine inspection which included a carb inspection replacing O-rings etc. I purchased a kit which was assembled by Bing out of Kansas and distributed by CPS. This kit included rubber bowl gaskets. I called them and we discussed my pass experience and he said these were the gaskets being used now. They are installed and working fine for the past 12 hours. Hope this didn?t cause mor confusion than help.
 
Keep in mind that carb float bowl is a very violent place especially in airplane environment. Air turbulence and rough ground operations slosh fuel in every direction inside the float bowl.

Not uncommon to have fuel appear at clear overflow tubing and deposit on drip tray.
 
For what?s worth

My experience was I purchased some after market rubber type gasket that were cheaper than what Lockwood sold the cardboard type gaskets. I?m not sure if these were Vitron.

I had some leaking issues, inconsist, holding most of the time but leaking others. A Rotax specialist felt I should go back to the Rotax OEM cardboard type gaskets and no issues since.

However I did the 400 hr engine inspection which included a carb inspection replacing O-rings etc. I purchased a kit which was assembled by Bing out of Kansas and distributed by CPS. This kit included rubber bowl gaskets. I called them and we discussed my pass experience and he said these were the gaskets being used now. They are installed and working fine for the past 12 hours. Hope this didn?t cause mor confusion than help.
 
Ppart number of kit please

Patrick - good info - please list the part number of the 'kit' and what is included in it. Thanks for the helpful info.
 
Of all the things that have caused us heartburn after the condition inspection, those flippin? carb bowl gaskets are pretty much the top of the list. It?s a rare year that I don?t end up needing to re-install them after the first engine start because of leaks. The stiff green ones seemed to be best for staying in place as the bowl is installed.
 
So what I have learned.........

The dye in the fuel tells me more than I would ever know.

I gave up last night after reassembling the bowls for the second time only to see the fuel weep out from under the gasket again....but I only could see that because of the dye and the black light.

Tonight I rechecked to see if any fuel would leak and there was no leaks. It seems that the gasket over 24 hours conforms and makes a seal.

I suspect everyone has a fuel weep immediately after a new gasket is installed but doesn't see it, the dye is the only reason I knew.

Viton gaskets are on the way, my feeling is they are the best solution.
 
Glad UV Tracer is working to help find leaks. Real eye opener...

Let us know what you find after a few flights. Particularly interested if fuel present at overflow/vent tubes.
 
I tried the elastomer gaskets (possibly Viton). They leaked like sieves. I have been reusing my green ROTX gaskets every annual for at least four years with no leaks.
 
I tried the elastomer gaskets (possibly Viton). They leaked like sieves. I have been reusing my green ROTX gaskets every annual for at least four years with no leaks.
I had no trouble at all with the green ones. The new rubber (Viton? Who knows?) gaskets may or may not seal up OK -- the real question is, can you get them to stay in place when installing the bowls. They seem to really want to slip out of place, causing terrible leaks. I finally resorted to a light film of Permatex Aviation Form-A-Gasket as a "glue" to hold them in place while installing the float bowls.

Cue the dire warnings that we'll all die in a fireball from doing this, but after a year and another condition inspection I feel fairly confident that we may live to see another day.

All in all, I'd rather go back to the green gaskets.
 
The instructor in the ROTAX course said he uses a dab of white grease to keep the gaskets in place while reinstalling the bowls.
 
Ref post #22 & #23

Sorry E B Eliot for the delay but here is the information you asked about, and maybe others would like to know.
Dual carb gasket kit for 912 from California Power Sport is p/n15-09421 and I believe it was $54. This is the kit I used at 400 hrs on my carbs.
However this kit came from ProCarb Shop, LLC, 13 Ram Ct. , Council Grove, KS 66846; ph#620-767-7844. This is where I called to discuss the the rubber bowl gaskets they provided in their kit as opposed to the green ones I’ve used before.

The p/n ProCarb uses for this kit is CV OHGK UL and the list of parts are as follows:
Quantity: 2 Carbs
“O Rings”
Biggest - Jet Stock
Next down - Throttle Shaft
Green - Choke Disc
4 small - Idle Jet & Idle Air Screw
Smallest - Jet Needle
And the two rubber bowl gaskets

FYI while replacing these all looked good except one of Idle Air O rings was obviously coming apart and needed to be replaced. Not that the others didn’t but that one was notable.

The guy I spoke with at ProCarb said they sell parts to the public and various distributors. He said feel free to call to see if they might have better pricing on Bing 64 carb parts.
 
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UPDATE;

The fuel smell is gone. As I stated it only smelled when the canopy was cracked on the step latch, usually during taxi after landing.

It ended up being the air vent line at the “T” in the overflow tube behind the gas tank bulkhead. The air vent line had come out of the T and this would occasionally allow gas to burp onto the skin inside the fuse area. Apparently with the canopy open the fumes would be sucked into the front area.

There is a pic in another post I made concerning the fuel vent.
 
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