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Smell gas in cockpit with full throttle in level flight. Normal?


gogogo888

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I rarely go full throttle in level flight, today I did some testing with different RPMs to get data for the Cruise speed thread. I noticed that whenever I go full throttle, I smell gas in the cockpit, my door doesnt close completely and has lot of air coming in. I'm wondering if smelling gas in cockpit is normal?

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IMO a smell of gas in the cockpit that is not identifiable with a benign cause (uncoordinated flight causing a small amount of fuel to exit the vents, for example), is cause for a precautionary landing as soon as practical. 

Could you smell gas on the ground, either with the engine stopped or running?

First thing I'd check is the sight tubes and the wing root fuel tank seals  behind them.  If you see any fuel streaks under the wing where they meet the fuselage, that's a telltale for those kind of leaks.  If not, I'd look at everything under the cowling very carefully.  If you see nothing there, I'd pull the center panel and look around the fuel valve, fuel filter, and attached hoses and clamps.

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12 minutes ago, FlyingMonkey said:

IMO a smell of gas in the cockpit that is not identifiable with a benign cause (uncoordinated flight causing a small amount of fuel to exit the vents, for example), is cause for a precautionary landing as soon as practical. 

The air was bumpy today, maybe fuel exited the vents? I had about 11 gallons on each tank.

Another instance I smelled gas was when I made a quick 30 degree turn to avoid traffic, I pushed full power, then I smelled gas. After a few seconds, I pulled back the throttle to 4,300 rpm and the smell went away.

 

14 minutes ago, FlyingMonkey said:

Could you smell gas on the ground, either with the engine stopped or running?

 

There were no gas smell on the ground with the engine running or stopped. The gas smell also goes away when rpm is around or below 5,200 rpm.

 

33 minutes ago, FlyingMonkey said:

First thing I'd check is the sight tubes and the wing root fuel tank seals  behind them.  If you see any fuel streaks under the wing where they meet the fuselage, that's a telltale for those kind of leaks.  If not, I'd look at everything under the cowling very carefully.  If you see nothing there, I'd pull the center panel and look around the fuel valve, fuel filter, and attached hoses and clamps.

I will check the fuel streaks under the wing tomorrow(I've seen it before when I over fill the tank). Will also open up the cowling and at everything very carefully.

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1 hour ago, Warmi said:

No.

My only experience with strong gas smell was due to a failed clamp on a fuel line to one of the carbs but my understanding is that generally you tend to smell gas when something is wrong with your carbs.

I will open up my cowling tomorrow to check the clamp on the fuel line to the carbs.

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If the fuel smell is in the cockpit and not outside in the engine compartment then my money lies with the fuel fitting coming out of the fuel sight tube bulkhead where the rubber fuel line attaches. You can see the 17mm nut.  This is the most common place for the slight fuel smell. Put your nose up in each sight tube opening and see if you can smell it more and take a flashlight and look for some tiny brown fuel stains if using auto fuel. There is a fix that does not require you to remove the bulkhead. You will have to pull the wing out some to get to this fitting. If you do this call me and I'll explain.

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7 hours ago, Roger Lee said:

If the fuel smell is in the cockpit and not outside in the engine compartment then my money lies with the fuel fitting coming out of the fuel sight tube bulkhead where the rubber fuel line attaches. You can see the 17mm nut.  This is the most common place for the slight fuel smell. Put your nose up in each sight tube opening and see if you can smell it more and take a flashlight and look for some tiny brown fuel stains if using auto fuel. There is a fix that does not require you to remove the bulkhead. You will have to pull the wing out some to get to this fitting. If you do this call me and I'll explain.

Thanks Roger, I will try to see if I can smell anything in the sight tubes tomorrow, I used auto fuel, will check for stains also.

I also noticed that in the last few flight, I got high fuel flow alert on my first take off, it went away after a few seconds and never reappear again, I wonder if all of these are related. 

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I had a similar issue and mine ended up being the carbs were overflowing, had the floats replaced and carbs serviced/sync'd issue never came back.  First indication was when I was practicing steep turns, second was working on side slips to align with centerline in cross winds and finally forward slips.  Note that there was a delay from the maneuver to getting the smell so I first assumed it was happening in level flight.

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2 hours ago, johnnyjr said:

I had a similar issue and mine ended up being the carbs were overflowing, had the floats replaced and carbs serviced/sync'd issue never came back.  First indication was when I was practicing steep turns, second was working on side slips to align with centerline in cross winds and finally forward slips.  Note that there was a delay from the maneuver to getting the smell so I first assumed it was happening in level flight.

I just had my carb synced 3 hours ago, engine was running very smooth.

Did your gas smell go away after a few seconds in level flight?

Did you smell gas after landing?

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The smell was on and off, I'd say after minutes SNL it would go away (needed time to stop overflowing, then evaporate completely).  After a few laps in the pattern working forward and side slips I called it a day when I smelled gas, parked, pulled my cowl and I had fuel puking from the overflow lines.  The fix was the float bowls and cleaning the carb for my issue.  Not sure if all CTs are the same, but my fuel overflow lines run into the bottom of the airfilter box, I had a puddle in the box (overflow was faster than the draining) when I parked and that made the issue obvious as far as where the fuel was coming from.

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1 hour ago, gogogo888 said:

No, they did not. The floats were replaced and weighted in May 2019, 6 grams each S/N 861-185.

Could the float be the problem?

Yes they could. I weigh floats every condition inspection. The fact that they were changed recently would even make them more suspect to me.

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6 hours ago, sandpiper said:

Weighing the floats is an easy check. Kinda like low hanging fruit. If that's not the problem then you haven't lost anything by checking.

 

7 hours ago, Tom Baker said:

Yes they could. I weigh floats every condition inspection. The fact that they were changed recently would even make them more suspect to me.

I just found Roger's video on how to check and take out the carb bowl. I will take out the floats to weight them.

Will also follow FlyingMonkey and Roger's advice to check the fuel sight tube for fuel streaks or smell.

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16 hours ago, gogogo888 said:

No, they did not. The floats were replaced and weighted in May 2019, 6 grams each S/N 861-185.

Could the float be the problem?

Could be, but they'd have to be *very* heavy.  I had both mine heavy and they were causing small amounts of fuel to accumulate in the drip trays, but I never smelled a thing.  If they are pushing enough to smell it, your carbs must be absolutely dumping fuel.

I agree it's an easy thing to check and eliminate.

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7 hours ago, gogogo888 said:

 

I just found Roger's video on how to check and take out the carb bowl. I will take out the floats to weight them.

Will also follow FlyingMonkey and Roger's advice to check the fuel sight tube for fuel streaks or smell.

Let the floats dry a few minutes before weighing.  You don't want the weight of any wet fuel on the outside of the float to affect your measurement.

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2 hours ago, Tom Baker said:

Probably not the sight tube, but rather the bulkhead fitting for the fuel line if there is a leak in the wing root. 

What Tom described above... happened to my plane.  Never smelled gas but I could see blue streaks (100ll in those days) that came through the wing tape.  FD USA fixed it.  

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