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912 Carbs

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tleiss(at)earthlink.net
Guest

Posted: Thu Mar 01, 2007 4:39 pm Post subject: 912 Carbs

Looking for some help.

  

 My Rotax 912UL is running very rough at Idle.  Also have fuel running out the vent tubes unless idle is above 2400rpm.    I have rebuilt both carbs (Bing 64) with kits from Bing.  Initial set-up as described in the Bing instructions.   I have synchronize the carbs with duel vacuum gauges.  However, adjusting the mixture screws has virtually no effect in RPM or the vacuum gauge readings.  Ignition is working fine, all new plugs.  All new connectors and good drop-offs when switching A or B (Mag Check).   

  

 I have compared my engines performance with two other 912 equipped planes on the field.  Mine is much rougher at low and medium speeds.

  

 One question is if the Carb piston vents go towards the intake manifold (as I have them) or the intake.

  

 Engine has 200 hours (192 by previous owner), 1 hour flight time since I've owned it and the rest are ground runs trying to get it running right.

  

 Thanks,

  

 Todd Leiss

 Kitfox IV Speedster

 N926JB  

 Merritt Island Florida

  

  

  

 

  [quote][b]

flier(at)sbcglobal.net
Guest

Posted: Thu Mar 01, 2007 6:53 pm Post subject: 912 Carbs

Todd,

  

 Fuel is running out the vent tubes due to the shaking of the  carbs.  The idle mixture needs to be established before syncing.  Be  sure the engine is at temp before trying to do any tuning.

  

 Do you have the Bing manual?  I rebuilt mine late last year  and it took some time to get them back into sync and running smoothly.   Give Bing a call.  Those guys are very helpful.

  

 Regards,

  

 Ted



   From: owner-kitfox-list-server(at)matronics.com  [mailto:owner-kitfox-list-server(at)matronics.com] On Behalf Of Todd  Leiss

Sent: Thursday, March 01, 2007 6:38 PM

To:  kitfox-list(at)matronics.com; rotax-list(at)matronics.com

Subject:  912 Carbs

 

 

 Looking for some help.

  

 My Rotax 912UL is running very rough at Idle.  Also have fuel running  out the vent tubes unless idle is above 2400rpm.    I have  rebuilt both carbs (Bing 64) with kits from Bing.  Initial set-up as  described in the Bing instructions.   I have synchronize the  carbs with duel vacuum gauges.  However, adjusting the mixture screws  has virtually no effect in RPM or the vacuum gauge readings.  Ignition  is working fine, all new plugs.  All new connectors and good drop-offs when  switching A or B (Mag Check).   

  

 I have compared my engines performance with two other 912 equipped planes  on the field.  Mine is much rougher at low and medium speeds.

  

 One question is if the Carb piston vents go towards the intake manifold (as  I have them) or the intake.

  

 Engine has 200 hours (192 by previous owner), 1 hour flight time since I've  owned it and the rest are ground runs trying to get it running right.

  

 Thanks,

  

 Todd Leiss

 Kitfox IV Speedster

 N926JB  

 Merritt Island Florida

  

  

  

 

[quote]



href="http://www.matronics.com/Navigator?Kitfox-List">http://www.matronhref="http://forums.matronics.com">http://forums.matronics.com



[b]

lcfitt(at)sbcglobal.net
Guest

Posted: Thu Mar 01, 2007 7:31 pm Post subject: 912 Carbs

Hi Todd,



I had the exact same problem after a rebuild with the Bing kit.  I traced it 

to the carb float needles.  Apparently they offer three types.  I don't 

recall which ones are which, although they can be identified by color.  The 

912ULS has a black one, Mine are yellow metal, as I recall and the other 

ones are white metal.



I finally had to go back to the old ones per the Rotax inspection 

procedures.  Smothed right out and no more fuel dripping.  The inspection 

procedure is issentially to look at the spring loaded pin end and if you see 

no wear under the crimp where the pin flange would be.  They are good to go. 

I called Bing and learned this stuff, but got no satisfaction.  That is why 

the change back to the old needles.



Regarding the guages.  It is my understanding that you set the cable lengths 

to balance the carbs.  The start point of the idle jets is 1.5 turns from 

full closed.  After the cables are adjused to balance the vacuum gauges, the 

jet can be tweeked to improve idle.  What you are doing in this procedure is 

making sure the throttle butterflys are opening at the same time, hence the 

vacuum gauges.



Lowell

---

tleiss(at)earthlink.net
Guest

Posted: Thu Mar 01, 2007 9:30 pm Post subject: 912 Carbs

Some more info on my carb problem:



My vent tubes are the proscribed length (about 4 inches), and tucked under

the float bowl spring clip.

I have new Boots or Flanges.

Vents under Carb inlets are free. Carbs are facing the correct way.

Synchronized by the Lockwood method (two Vacuum gauges) adjusting the

throttle cables as described in a "power-up" article.



On the bottom of the Carb slide (with long needle valve set at proscribed

clip position) there are two vent holes.  Do these face the air filter or

Intake manifold (as I have them)?



I have a new (Jan 07) Fuel pump from Lockwood.  I had ignition issues,

which I solved, but around the same time my old fuel pump started to leak. 

The carbs didn't have the fuel running out the vents before the new pump,

but it never occurred to me that the pump could be the problem.  This may

very well be the issue.  I will definitely check with Lockwood tomorrow

concerning the fuel pressure.



Keep the wonderfully helpful cards and letters coming.



All the Best,



Todd



       

 	  Quote: 	
		   [Original Message]

 From: Roger Lee <ssadiver1(at)yahoo.com>

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

 Date: 3/1/2007 10:15:21 PM

 Subject: RotaxEngines-List: Re: 912 Carbs



 



 Hi Todd,

 Question:  Are both carbs actting up in the same way?



 Those vents you describe on the carb throat edges are actually inlets.

They must face out towards the air cleaner side or you will have the
	


problems as you describe. These intakes help work the diaphram in the top

of your carb for pressure changes. 

 	  Quote: 	
		  

 If this was the problem your home free, if not:

 One of the things you need to check is your fuel pump pressure. There is

a new service bulletin out on certain serial numbered engines that they
	


want these pumps replaced. The symptoms are as you describe. The max

pressure (without the manual in front of me) is 5.6 psi and some of these

pumps are putting out in the 9psi range.

 	  Quote: 	
		   This type of pressure will cause what you have described. There is a

replacement program as I understand it.
	


 	  Quote: 	
		   Your mixture screw should be set at 1.5 turns and left alone. Then you

should set the carb's idel screw with the engine off and then while it is
	


running.

 	  Quote: 	
		  



 My bet is that your carbs are facing the wrong way.



 Good luck!



 --------

 Roger Lee

 Tucson, Az.





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=98230#98230

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Fri Mar 02, 2007 5:43 am Post subject: 912 Carbs

The two stroke Bing carbs now have a tube which connects the left bowl vent

with the right bowl vent and then a couple of small holes pierced through

the tubing near the bottom of the loop.  This was done to keep air from

blowing gas out of the bowls.  It's just an Idea but it may just work for

you too.



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

kitfoxmike

Joined: 05 Dec 2006
Posts: 373

Posted: Fri Mar 02, 2007 7:03 am Post subject: Re: 912 Carbs

The float needles that I used were the 261-705 from ACS there are about 15 ea.  I removed my spring clips on both sides, I felt they were keeping things from working right, lockwood said those are only there for install ease.  If you find any particals in the fuel in the bowls, two things to do. replace all hoses with auto fuel injection hose, next put small rock filters just before the carbs. These needles have a black tip, rubber.  Lockwood said that the black is the best, has the strongest spring inside.



On adjusting the carbs, I've never had good luck with the vacuum deal.  What I do is open the throttle all the way and then check at the carbs to make sure the levers are the same against the stop, I have mine set up to be about 1/32 to 1/64 end gap on both sides. This should get you real close, and then put the idle stop the same on both sides, loosen up the stop and bring it to the arm and go the same amount of turns to set the idle.

flier(at)sbcglobal.net
Guest

Posted: Fri Mar 02, 2007 7:56 am Post subject: 912 Carbs

The fuel running out your vents is due to shaking of the carbs (most likely)

or the floats set too high.  



--

kitfoxmike

Joined: 05 Dec 2006
Posts: 373

Posted: Fri Mar 02, 2007 9:39 am Post subject: Re: 912 Carbs

Or the float needle stuck open, been there.

pulsair(at)mindspring.com
Guest

Posted: Fri Mar 02, 2007 11:24 am Post subject: 912 Carbs

Or the choke is stuck.



---

barry(at)pgtc.com
Guest

Posted: Fri Mar 02, 2007 2:22 pm Post subject: 912 Carbs

Some shaking, vibration, can cause the gasoline to foam which causes it to 

come out of the overflow tube.



Barry West



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