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  #1  
Old 05-19-2011, 12:36 PM
MartySantic's Avatar
MartySantic MartySantic is offline
 
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Location: Davenport, IA
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Default Carburetor Problem? Gasoline/Fuel Smell During Test Flight

Last week before leaving to witness the space shuttle launch, I flew the RV-12 after replacing the prop hub and adjusting the prop pitch. After climbout, I flew for about a minute at WOT (5600 rpm). After reducing the power I noticed a gasoline smell which lingered and it coincided with what felt like a momentary engine miss or shudder. I immediately reduced power and headed back to the airport. The same happened on my return to the airport.

After landing I immediately pulled the top cowl. The was ZERO evidence. No gasoline smell in the cockpit, in the engine compartment, the air filter, the fuel pump, or the carburetor overflow tube. The carb tray was dusty and there was no evidence of gas spilling onto the tray and creating a track in the dust.

With assistance, started the engine and ran the engine (on the ground) at various power settings to WOT for about 20-30 seconds with a friend observing the engine. Zero evidence of a fuel leak at the carb, the overflow tube, the fuel pump or any of the connections/fittings. There was no gasoline smell. No evidence of an engine miss on the ground. The gascolator sample was clean before the test flight.

Help! I am looking for troubleshooting ideas!! Based on a couple of previous threads.....carb float problem (but, it self corrected)? speck of dirt in the carb needle valve?

Will pull the bottom cowl today and continue to look. Hesitant to fly until I find something.
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Marty Santic ----- W9EAA
RV-12 N128MS ----- Now Flying
My RV-12 Build Log - http://www.martysrv12.blogspot.com/
Davenport, IA

Last edited by MartySantic : 05-19-2011 at 12:40 PM.
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  #2  
Old 05-19-2011, 01:41 PM
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DonFromTX DonFromTX is offline
 
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Location: La Feria Texas
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Default

I have found that ALL aircraft engines seem to shudder when I smell fuel
With the tank and many feet of fuel supply and return lines going thru the cockpit not to mention the fuel pump, shutoff valve, and fuel flow sensor, it may be prudent to pull some inside panels and look for evidence of leaking there as well.
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  #3  
Old 05-19-2011, 01:53 PM
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Jetguy Jetguy is online now
 
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Default More info requested!

What were the indications on your EMS? Any alarms going off. Loss of Fuel Pressure or anything else? If your don't remember then try down loading your Dynon on to computer to check. If you have a long runway I would try another flight if you cant reproduce it on the ground. On takeoff if you get good power climb at Vx to altitude and circle the airport. if you experience a loss of engine power at full throttle and an indication of a loss of Fuel Pressure then my money is on the fuel pump. It can fail with such a small leak that by the time you check it could have evaporated. How many hours on engine. What kind of fuel? Did the engine run smoother at lower power settings?
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RV12 N1212K
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Johnrv12@icloud.com
RV14 Wing, arrived and building at Rdog's new Hanger at 16X
S/N 140014
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  #4  
Old 05-19-2011, 02:10 PM
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MartySantic MartySantic is offline
 
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Quote:
Originally Posted by DonFromTX View Post
I have found that ALL aircraft engines seem to shudder when I smell fuel
With the tank and many feet of fuel supply and return lines going thru the cockpit not to mention the fuel pump, shutoff valve, and fuel flow sensor, it may be prudent to pull some inside panels and look for evidence of leaking there as well.
If I had a leak in the fuselage, I would expect the smell to linger with the canopy cllosed. No such smell. But will pull panels and check the fittings.

Quote:
Originally Posted by Jetguy View Post
What were the indications on your EMS? Any alarms going off. Loss of Fuel Pressure or anything else? If your don't remember then try down loading your Dynon on to computer to check. If you have a long runway I would try another flight if you cant reproduce it on the ground. On takeoff if you get good power climb at Vx to altitude and circle the airport. if you experience a loss of engine power at full throttle and an indication of a loss of Fuel Pressure then my money is on the fuel pump. It can fail with such a small leak that by the time you check it could have evaporated. How many hours on engine. What kind of fuel? Did the engine run smoother at lower power settings?
There were no alarms on the Dynon. All parameters seemed to be normal. On takeoff had a good climb at Vy, 5150 rpm. 100 hours, using MOGAS. I will download the Dynon log. Can a fuel pump problem be intermittent and self correcting? The shudder was momentary and it is hard to say if reducing the throttle helped matters.
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RV-12 N128MS ----- Now Flying
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Davenport, IA

Last edited by MartySantic : 05-19-2011 at 02:15 PM.
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  #5  
Old 05-19-2011, 03:11 PM
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Jetguy Jetguy is online now
 
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Default Get that problem to reproduce!

If your engine runs ruff at full power but when throttled back it smooths out and runs fine that could be a fuel pump. You would also see a loss of fuel pressure and an increase in fuel flow to the red line. You need to figure out a way to try to reproduce the problem. Until then we are just guessing.
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RV12 N1212K
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RV14 Wing, arrived and building at Rdog's new Hanger at 16X
S/N 140014
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  #6  
Old 05-19-2011, 03:31 PM
DEWATSON DEWATSON is offline
 
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Location: Quincy, Florida
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Default smell

I know that there are obvious differences between the RV12 and the RV8, but this is what I found when the smell of gasoline scared me to death.

The fuel tank vent line openings are directly beneath the pilots seat on the underside of the fuselage. At different times I would catch a whiff of fuel. I found out that the only time I ever smelled it was when both tank were packed full and I made a turn in one direction or the other. Fuel would leak from the high tank vent opening and I could smell it inside the cockpit even though I was moving through the air at cruise speed. It never does it unless the tanks are very close to full. These vent line openings are facing forward and are somewhat "pressurized" by the air as the airplane flies through the air. Evidently the pressure in the tank is greater when the fuel is aggitated and there is very little air in the high tank. Just my experience for what it's worth.
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  #7  
Old 05-19-2011, 05:32 PM
N223JH N223JH is offline
 
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Location: Boerne, TX
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Default Data Download?

Marty, if you haven't already, pull the data from the Dynon and look closely at the fuel pressure and fuel flow at the time of the incident. If your engine-driven pump dumped fuel (the odor) it will be reflected in data. (FP down, FF up.) Unfortunately car gas will not leave distinctive blue stains on the weep holes on the pump. If you swab the weep holes carefully, you may be able to pick up a yellow stain. You might also check the carb vents (clear hoses) in case some kind of over-pressure caused them to barf fuel.

FWIW, Rotax tech told me authoritatively that pump does *not* have an intermittant failure mode.

Jim
RV12 flying 30 hours
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  #8  
Old 05-19-2011, 06:25 PM
Dave12 Dave12 is offline
 
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Location: Elkton, Md.
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I don't have anything to add to the good advice you have already received, but the fact that the electric fuel pump is energized all the time has always struck me as odd. Does anyone know if the cert. aircraft that use the Rotax have this full time redundancy? As most know, the use of aux. elect. fuel pumps is nothing new and very effective. The mechanical fuel pump on the Rotax seems to be suspicious at the very least. Good luck, if anyone will figure this out, I know you will.
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  #9  
Old 05-19-2011, 07:53 PM
Mich48041 Mich48041 is offline
 
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Location: Riley TWP MI
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Default Vapor Lock ?

Marty,
What was the outside air temperature? A RV-12 owner in Texas experienced vapor lock shortly after takeoff. He was burning auto fuel also. His engine sputtered at full throttle but ran fine at reduced throttle. When it is hot inside of the cowl, the fuel can vaporize inside of the fuel lines between the gascolator and engine driven fuel pump. That gasoline vapor can escape out of the carburetor vents without leaving a trace in the drip pan. A shroud around the gascolator along with a scat tube supplying cooling air will help. I am not saying your fuel problem is due to vapor lock, only that it is a possibility. If the Dynon data log shows a drop in fuel pressure and an increase of fuel flow at the time of the problem, then suspect either vapor lock or a fuel leak.
Here is an idea that I had but have never tried: A very small piece of Styrofoam placed under the engine fuel pump weep holes will melt if gasoline drips onto it.
The gascolator screen should be checked also.
Joe Gores

Last edited by Mich48041 : 05-19-2011 at 07:59 PM. Reason: Added check gascolator screen
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  #10  
Old 05-19-2011, 08:22 PM
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MartySantic MartySantic is offline
 
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Default

Downloaded the data from the Dynon. Something was most definitely going on with fuel flow and fuel pressure. I have attached 4 plots. The 1st is from a month ago. The 2nd is a test flight where I experienced no problems. The 3rd is the test flight where I experienced the gas smell. And the 4th is from the ground run after removing the top cowl, immediately after landing in an attempt to resolve the problem. No gas smell was observed during the ground run.

https://picasaweb.google.com/lh/phot...eat=directlink

https://picasaweb.google.com/lh/phot...eat=directlink

https://picasaweb.google.com/lh/phot...eat=directlink

https://picasaweb.google.com/lh/phot...eat=directlink

Any insight?
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Marty Santic ----- W9EAA
RV-12 N128MS ----- Now Flying
My RV-12 Build Log - http://www.martysrv12.blogspot.com/
Davenport, IA

Last edited by MartySantic : 05-20-2011 at 12:24 PM. Reason: Added a Plot
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