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912s carb leak

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Lyle Persels

Joined: 10 Jan 2006
Posts: 34
Location: Osceola, IA

Posted: Tue Sep 13, 2011 1:06 pm Post subject: 912s carb leak

My 912S leaks fuel quite heavily from the vent line when the engine is running. The float needle valve seems to be unobstructed and closing properly. What else should I look for.



Lyle Persels

Osceola, IA

KF-IV 1200 912ULS

450 Hrs

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Roger Lee

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

Posted: Tue Sep 13, 2011 4:17 pm Post subject: Re: 912s carb leak

Hi Lyle,



A few things may cause this. Fuel level too high in the bowl, float needle not seating properly. It may be a good idea to replace these if the engine is very old. If it is just one leaking then a possible blockage at the needle. Carbs not synced which cause a rougher than normal engine and the shake makes fuel vent. I would do it in this order. Sync the carbs, check the fuel level and replace the float needle. You can't necessarliy tell if a float needle is bad just by looking at it.

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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
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Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Wed Sep 14, 2011 2:38 am Post subject: 912s carb leak

If you sync the carbs and one...or more...is leaking, you'll end up  

doing it all over again after replacing the needle.....and seat  

(which I would do).



Lynn Matteson

Kitfox IV Speedster, taildragger

Jabiru 2200, #2062

Prince prop 64 x 30, P-tip

Electroair direct-fire ignition system

Rotec TBI-40 injection (sleeved to 36mm)

Status: flying with "Ramcharger" intake manifold...1173 hrs (since  

3-27-2006)





On Sep 13, 2011, at 8:17 PM, Roger Lee wrote:



 	  Quote: 	
		   



 Hi Lyle,



 A few things may cause this. Fuel level too high in the bowl, float  

 needle not seating properly. It may be a good idea to replace these  

 if the engine is very old. If it is just one leaking then a  

 possible blockage at the needle. Carbs not synced which cause a  

 rougher than normal engine and the shake makes fuel vent. I would  

 do it in this order. Sync the carbs, check the fuel level and  

 replace the float needle. You can't necessarliy tell if a float  

 needle is bad just by looking at it.



 --------

 Roger Lee

 Tucson, Az.

 Light Sport Repairman - Maintenance Rated

 Rotax Repair Center - Heavy Maint. Rated

 Home 520-574-1080  TRY HOME FIRST

 Cell 520-349-7056





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=352212#352212

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Lynn
Kitfox IV-Jabiru 2200
N369LM

egp8111

Joined: 25 Mar 2010
Posts: 49

Posted: Wed Sep 14, 2011 5:03 am Post subject: Re: 912s carb leak

I've recently got the carbs out of balance while syncing them a few days ago.  When the engine ran rough one carb started venting gas out of the vent line.  When I got the engine smoothed out the venting stopped.  Obviously the vibration caused the carb to vent fuel.  However it made me get busy and install a catch system for any fuel that the carb vented.  Last thing you need is an engine to start running rough and then leaking fuel on the exchaust !

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Roger Lee

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

Posted: Wed Sep 14, 2011 11:54 am Post subject: Re: 912s carb leak

You can't just put those vent tubes anywhere. Not in any low or high pressure areas. No dead end bottle. They must be open to the air. You can run them into your airbox or extend the tubes down the cowl, but they must get equal pressure or your engine will run rough. See the installation manual or some of the guys here can tell you where they mounted their's.

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_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056

egp8111

Joined: 25 Mar 2010
Posts: 49

Posted: Thu Sep 15, 2011 5:26 am Post subject: Re: 912s carb leak

I located a metal container that looks like a cat food can (well actually it is a cat food can) It fits nicely around the bottom of the carb.  I installed a 1/4 tube from the bottom to connect a drain line which I routed away from the exhaust but not into the airstream. Then I covered the outside bottom and sides of the can with a heat reflective tape.  The carb vent lines run into the open top of the can by the float bowl.  They are the original length and open to the ambient air.  The can serves the dual function of a heat shield and a drip catcher.  I havent seen any change in engine preformance since I installed them.    Anyone see any obvious problems with this set up or am I headed for a "cat"astrophe.  (sorry couldn't resist)

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Av8r3400

Joined: 22 Sep 2008
Posts: 83
Location: North Central Wisconsin (KRRL)

Posted: Thu Sep 15, 2011 8:53 pm Post subject: Re: 912s carb leak

If you extend the vent tubes, take care they will siphon fuel out of the float bowls.  A friend had this happen on his RANS S7.  Once they cut the vents back, draining them into a drain pipe (larger diameter than the tube) all was well again.

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Thanks,
Av8r3400

Kitfox Model IV-1200 W/912UL & IVO
Kitfox Model IV-1050 W/912UL & Warp
YouTube Videos

lcfitt(at)sbcglobal.net
Guest

Posted: Fri Sep 16, 2011 6:31 am Post subject: 912s carb leak

This is what I recall as well.  No personal experience with it, but in the 

day, I think it was Eric Tucker that said don't modify them.  I think he 

referred to them as pressure compensating tubes.  We call them drip tubes 

because that is our experience.  I bought a couple of very small Stainless 

funnels that I plan on mounting just below the tubes to catch any overflow. 

I have experienced dripping after a carb rebuild.  It seems the new needles 

were not sealing well.  Lots of rough running at idle and gas on the ground. 

Then I had the pans under the carbs, but those  were a nuisance when 

removing the float bowl and servicing.  Just in the way big time.

Lowell



--------------------------------------------------

From: "Av8r3400" <theav8rweb(at)yahoo.com>

Sent: Thursday, September 15, 2011 9:53 PM

To: <kitfox-list(at)matronics.com>

Subject: Re: 912s carb leak



 	  Quote: 	
		   



 If you extend the vent tubes, take care they will siphon fuel out of the 

 float bowls.  A friend had this happen on his RANS S7.  Once they cut the 

 vents back, draining them into a drain pipe (larger diameter than the 

 tube) all was well again.



 --------

 Thanks,

 Av8r3400



 Kitfox Model IV-1200 W/912UL &amp; IVO

 Kitfox Model IV-1050 W/912UL &amp; Warp



 Read this topic online here:



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