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912 Question - Gas dripping from the Carbs

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Dennis.Kirby(at)kirtland.
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Posted: Tue Mar 31, 2009 11:03 am Post subject: 912 Question - Gas dripping from the Carbs

Classification:  UNCLASSIFIED  

 

  

Fellow 912 Drivers –  

   

Looking for your collective experiences to help me solve this 912ul mystery.  

Last week, after returning from a 2-hour flight in my Mark-3, I noticed gas dripping from one of the air filters.  

This has never happened before, so I am baffled as to what might’ve caused this.  

   

Here are some specifics of the flight, that might offer clues:  

I was flying at a higher-than-normal (for me) power setting that day – 5100 rpm.  

My auxiliary (electric) fuel pump was operating the whole time.  It’s a Facet –same as what many of us use.  

I also discovered fuel in the carb overflow hose – the little 1/8 inch clear tube that comes out from the carb.  

   

It only dripped for a minute or two after engine shutdown, then stopped.  

The engine seemed to run fine the entire flight.  

I suspect that the combination of 5100 rpm, plus having the electric fuel pump running, might have caused excess fuel in the carb, thus overflowing it.   But I don’t know this for sure.  

   

Any clues?  

   

Many thanks –  

Dennis Kirby  

Cedar Crest, NM  

      

Classification:  UNCLASSIFIED   

 

  [quote][b]

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zeprep251(at)aol.com
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Posted: Tue Mar 31, 2009 2:17 pm Post subject: 912 Question - Gas dripping from the Carbs

The only way fuel gets into the air filter is past the needle and seat.It has to fill the float bowl high enough to be pushed out of the main jet discharge.More pressure than the needle can handle,perhaps because of the use of the aux pump.There are different size needles and seats for higher pressure systems with the Bing 64CV.The residual pressure in the pump and hoses will force fuel past the seat until the pressure equalizes atmospheric.   

 

   G Aman MK 3 C 2200 Jabiru Bing 64CV

 

   

 

   

 

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lucien

Joined: 03 Jun 2007
Posts: 721
Location: santa fe, NM

Posted: Tue Mar 31, 2009 3:25 pm Post subject: Re: 912 Question - Gas dripping from the Carbs

 	  Dennis.Kirby(at)kirtland. wrote: 	
		    

 

  

Fellow 912 Drivers –  

   

Looking for your collective experiences to help me solve this 912ul mystery.  

Last week, after returning from a 2-hour flight in my Mark-3, I noticed gas dripping from one of the air filters.  

This has never happened before, so I am baffled as to what might’ve caused this.  

   

Here are some specifics of the flight, that might offer clues:  

I was flying at a higher-than-normal (for me) power setting that day – 5100 rpm.  

My auxiliary (electric) fuel pump was operating the whole time.  It’s a Facet –same as what many of us use.  

I also discovered fuel in the carb overflow hose – the little 1/8 inch clear tube that comes out from the carb.  

   

It only dripped for a minute or two after engine shutdown, then stopped.  

The engine seemed to run fine the entire flight.  

I suspect that the combination of 5100 rpm, plus having the electric fuel pump running, might have caused excess fuel in the carb, thus overflowing it.   But I don’t know this for sure.  

   

Any clues?  

   

Many thanks –  

Dennis Kirby  

Cedar Crest, NM  

	


There was a service bulletin on the 912 fuel pump (I believe it was the FP) a while back where a possible overpressure situation could develop when an auxiliary electric pump is used. 

Can't remember if it was both the 80 and 100hp engines...



You might check through the bulletins on rotax-owner.com and see if your engine is affected. I think you had to replace the fuel pump to comply with it.



Otherwise, could just be a sticky float valve. I had one of the float bowl pins bent on one of my carbs when I first got mine, no idea how it got bent, but it made it so only one float was actually functional. The motor ran perfectly, but there was always a fine layer of gas on the float bowl after flying that I simply didn't notice for a while.  Replaced the bowl and that fixed it.



LS

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Posts: 1246

Posted: Tue Mar 31, 2009 4:35 pm Post subject: Re: 912 Question - Gas dripping from the Carbs

 	  Dennis.Kirby(at)kirtland. wrote: 	
		  

I suspect that the combination of 5100 rpm, plus having the electric fuel pump running, might have caused excess fuel in the carb, thus overflowing it.   But I don’t know this for sure.  

   

Any clues?  

   

	




Running the engine at a higher RPM should not cause any increase in fuel pressure to the carbs.  If you have the correct pressure rating electric pump, running that the entire time should not cause gas to leak out the carb.  With the correct facet fuel pump installed, the pressure to the carb is the very close to the same weather the electric pump is turned on or off.  Assuming you have the correct pressure facet electric pump, and assuming it has not been causing this fuel overflow in the past, I see no reason to suspect it now.



From what you describe, the float bowl of your carb is overfilling and letting it leak out of the carb at places you describe.  It sounds like a stuck float or stuck float valve to me.  I would also check the vitreon valve tip material on the carb float valve to make sure it is in good condition and capable of shutting off the gas in the float chamber to prevent overfilling of the float bowl.   



Mike

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Wed Apr 01, 2009 4:10 am Post subject: Re: 912 Question - Gas dripping from the Carbs

Dennis,



As others have stated, the Viton tipped float valve is probably not sealing properly. They do wear out in time  and/or sometimes a tiny bit of debris can settle between the float valve and seat. If you don't have one already, pay $10 for a Bing Manual at 

http://www.bingcarburetor.com/manual.html 

and dig into the carbs (one at a time). If you have a few hundred hours or more on these carbs, it is probably time to do an inspection, cleaning and selective seal and parts replacement anyway.

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Roger Lee

Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.

Posted: Wed Apr 01, 2009 8:37 am Post subject: Re: 912 Question - Gas dripping from the Carbs

Thom and Mike both have good points.

A little wear on the needle valve attached to the floats to shut off the fuel, plus maybe more vibration at 5100 in your particular plane (for whatever reason i.e. prop or carb balance) and running an electric pump in series verse parallel could all add up to fuel bypassing the needle valve shut off in the carb and puking out the tube and or air intake.

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Dennis.Kirby(at)kirtland.
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Posted: Wed Apr 01, 2009 9:47 am Post subject: 912 Question - Gas dripping from the Carbs

Classification:  UNCLASSIFIED  

 

  

Thanks to the 912 guys who responded to my question with good advice!  

   

Gary A. – I think you are right … the likely culprit is my electric fuel pump pushing too much gas thru the carbs.  I will try flying with the electric Facet “off” and see what happens.  I may also consider plumbing my auxiliary fuel pump in parallel rather than in series, like it is now.  

   

Lucien – Good idea to look inside the float bowls – see if I have any stuck floats or bent pins.  

   

Mike B. – Again, good tips about a potential overpressure from the Facet pump, as well as a possible stuck float.  

   

I’ll address each of these ideas one at a time, and report back to the List when I discover the fix.  

   

Dennis Kirby  

Cedar Crest, New Mexico  

      

Classification:  UNCLASSIFIED   

 

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zeprep251(at)aol.com
Guest

Posted: Wed Apr 01, 2009 2:27 pm Post subject: 912 Question - Gas dripping from the Carbs

To all,

   Just a little trick for flooding problems.If a piece of debris gets stuck in the seat and is held there by the pressure exerted on the needle by higher than normal fuel level,,just clamp off the fuel line and let the engine run until it is ready to quit.You can usually tell when it leans out and picks up a few RPM.Now the fuel bowl is near empty,but of more importance, the needle has dropped clear of the seat,and by releasing the clamp, a rush of fuel will clear the debris out of the seat and off the needle.Like Beauford says,worth what ye paid for it.

       G Aman MK-3C Jabiru 2200A Bing 64CV

 

   

 

   

 

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