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912 rough running below 3000 rpm
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flynn elliott

Joined: 23 Jun 2007
Posts: 20
Location: SOUTH AFRICA

Posted: Fri May 22, 2015 8:11 am Post subject: 912 rough running below 3000 rpm

Hi Guys, could really use some help with a 912s.

After leaving my Foxbat for two months , she started up just fine as usual but ran as rough as hell untill 3000rpm and up where the motor runs smooth as silk.

As always the fuel had been drained and fresh put in after the layup. We have since cleaned the carbs, put new float bowl gaskets, a fresh set of plugs and had my A P balance the carbs, which were real close anyway.

The start up is instant as always has been, the mag drop is inconsistant, sometimes between 100 and 200  and very rough below below 3000rpm yet back to its usual 50rpm drop above.

Original plugs went back in and gave the same result.

I flew for half an hour yesterday in the hope of clearing the problem but no way, as I closed the throttle for landing we were back to a very rough motor.

Any help would be more than appreciated.

Thanks 

Flynn

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Fri May 22, 2015 8:25 am Post subject: 912 rough running below 3000 rpm

Insure both idle jets are completely open.



Over the years I have discovered a rough or no run 912ULS below 3000 rpm is

idle jet related.



Idle jet is extremely small.  A tiny bit of trash makes a lot of difference

on fuel flow.



For what it is worth.



john h

mkIII

Titus, Alabama



--

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

flynn elliott

Joined: 23 Jun 2007
Posts: 20
Location: SOUTH AFRICA

Posted: Fri May 22, 2015 10:20 am Post subject: 912 rough running below 3000 rpm

Thanks John, will pull them out and double check Again .



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John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Fri May 22, 2015 10:57 am Post subject: 912 rough running below 3000 rpm

I run a single strand copper wire through them to insure they are clean.

Copper won't scratch the jet.



john h

mkIII

Titus, Alabama



--

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

flynn elliott

Joined: 23 Jun 2007
Posts: 20
Location: SOUTH AFRICA

Posted: Fri May 22, 2015 11:46 am Post subject: 912 rough running below 3000 rpm

Good thought John

Thanks



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Roger Lee

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

Posted: Fri May 22, 2015 2:22 pm Post subject: Re: 912 rough running below 3000 rpm

I agree. Pull the idle jet and run a small strand of copper wire through the extremely tiny hole in the center. You may need to do the same with the mixture orifice located in the corner of the bowl.

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

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Fri May 22, 2015 2:34 pm Post subject: Re: 912 rough running below 3000 rpm

Roger, I always called that the "enricher jet" in the "enricher well".  Have no idea what the correct nomenclature of them are.



I iced up the idle jets on my 912ULS in 2000 going in to Toad River, BC.  Engine quite as soon as it went through 3,000 rpm.  Would start and run normal above 3,000, but not below it.  Went across the Alaska Highway, got a cup of coffee, came back and the engine idled like a sewing machine.  Conditions were conducive to icing.  Learned then that 912's don't like the idle jet to be out of tune.

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

flynn elliott

Joined: 23 Jun 2007
Posts: 20
Location: SOUTH AFRICA

Posted: Fri May 22, 2015 9:32 pm Post subject: 912 rough running below 3000 rpm

Thanks Roger, as soon as I can escape from work I will do just that and give

feed back.

Flynn



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mortweaver

Joined: 25 Apr 2015
Posts: 22

Posted: Sat May 23, 2015 8:27 am Post subject: 912 rough running below 3000 rpm

I have seen the problem you have described.  When a carb idle jet becomes blocked, the engine will shake at RPM below 3,000.  Then the floats of both carbs begin to bounce, which contributes to the engine running rough (floats become incompetent).  By removing the float bowls of both carbs you can remove the idle jet in each carb for inspection under a bright lite.  I found a very small spec of fuel hose lining blocked a jet on one of my carbs.  Probably happened when I installed a carb fuel hose on a barb fitting.

Dave Weaver N912GR

  



     On Friday, May 22, 2015 2:52 PM, Flynn Elliott <foxflynn(at)worldonline.co.za> wrote:

  

  



 --> RotaxEngines-List message posted by: "Flynn Elliott" <foxflynn(at)worldonline.co.za (foxflynn(at)worldonline.co.za)>



Good thought John

Thanks



--

_________________
Dave Weaver

flynn elliott

Joined: 23 Jun 2007
Posts: 20
Location: SOUTH AFRICA

Posted: Sat May 23, 2015 12:29 pm Post subject: 912 rough running below 3000 rpm

Hi Dave,

Thanks for your input, every one seems to be in the same mind over this issue. Will get on it asap and report back .

Flynn



Sent: 23 May 2015 06:26 PM

To: rotaxengines-list(at)matronics.com

Subject: Re: 912 rough running below 3000 rpm

 

I have seen the problem you have described.  When a carb idle jet becomes blocked, the engine will shake at RPM below 3,000.  Then the floats of both carbs begin to bounce, which contributes to the engine running rough (floats become incompetent).  By removing the float bowls of both carbs you can remove the idle jet in each carb for inspection under a bright lite.  I found a very small spec of fuel hose lining blocked a jet on one of my carbs.  Probably happened when I installed a carb fuel hose on a barb fitting.



Dave Weaver N912GR



 

 



On Friday, May 22, 2015 2:52 PM, Flynn Elliott <foxflynn(at)worldonline.co.za (foxflynn(at)worldonline.co.za)> wrote:



 

--> RotaxEngines-List message posted by: "Flynn Elliott" <foxflynn(at)worldonline.co.za (foxflynn(at)worldonline.co.za)>



Good thought John

Thanks



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rampil

Joined: 04 May 2007
Posts: 870

Posted: Sat May 23, 2015 9:03 pm Post subject: Re: 912 rough running below 3000 rpm

Here's another thought.



At mid range or less throttle, one of the carb

slides may stick in the barrel, unbalancing

the engine.  Did you A&P try balancing 

down in the throttle range where you see the

trouble?

_________________
Ira N224XS

vernon11

Joined: 03 Aug 2010
Posts: 14

Posted: Sun May 24, 2015 12:19 am Post subject: 912 rough running below 3000 rpm

Yes I did. We are now going to strip everything, to see if possibly there is 

a bit of junk floating around somewhere.



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

From: "rampil" <ira.rampil(at)gmail.com>

Sent: Sunday, May 24, 2015 7:03 AM

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

Subject: Re: 912 rough running below 3000 rpm



 	  Quote: 	
		   



 Here's another thought.



 At mid range or less throttle, one of the carb

 slides may stick in the barrel, unbalancing

 the engine.  Did you A&P try balancing

 down in the throttle range where you see the

 trouble?



 --------

 Ira N224XS





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=442517#442517

Roger Lee

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

Posted: Sun May 24, 2015 2:54 pm Post subject: Re: 912 rough running below 3000 rpm

Blow the carbs out with carb cleaner and then follow it with air pressure air. Don't blow against the diaphragm with high pressure air.

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

flynn elliott

Joined: 23 Jun 2007
Posts: 20
Location: SOUTH AFRICA

Posted: Sun May 24, 2015 10:23 pm Post subject: 912 rough running below 3000 rpm

Good advice, thanks Roger.



--

flynn elliott

Joined: 23 Jun 2007
Posts: 20
Location: SOUTH AFRICA

Posted: Tue Jun 02, 2015 7:49 am Post subject: 912 rough running below 3000 rpm

Latest update,

Idle jets cleaned, copper wire passed through although nothing appeared in

terms of crud, ran motor seemed better, closed throttle for landing and we

were back to rough running.

This morning pulled idle jets again, able to see through one but not the

other. Cleaned the hell out of it over a white cloth yet no crud seemed to

appear although I can now clearly see through it.

Motor now idles at 1800 rpm reasonably well yet appears to be hunting

slightly whether on left mag, right mag, or both, mag drop 50rpm both. 

All cables smooth and returning to stops.

Fuel lines flushed.

Fresh fuel.

Fresh filter 

New plugs.

Maybe I am looking for a smooth smooth 912 idle that doesn't exist, we don't

have another at the field to compare.

It has been suggested that ignition packs are at fault although that seems

highly unlikely as the motor starts on the click and cruises super smooth.

Many thanks to all for help and suggestions.

Flynn

--

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Tue Jun 02, 2015 8:34 am Post subject: 912 rough running below 3000 rpm

Saw this kind of thing once on an aircraft that sat a while with auto 

fuel in the tanks. The evaporating fuel left some residue which then 

re-liquified somewhat in the new fuel and wreaked havoc on the fuel 

system. Problem was the evidence was very hard to see and the effects 

very subtle, as the residue basically "plated" the entire fuel system 

with a very light coating of sludge, which would, after some hours, 

always lead to either a fuel filter clogging, or a jet clogging, or 

something similar. The only solution was to put a Facet fuel pump on the 

tank exit line and re-circulate fuel through the tank for days on end, 

replenishing the fuel occasionally, to clean out the tank sludge. I hope 

this isn't your problem but I thought I'd put it out there.



Guy Buchanan

Ramona, CA

Kitfox IV-1200 / 912-S / Warp 3cs / 500 hrs. and grounded

Now a glider pilot, too.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

flynn elliott

Joined: 23 Jun 2007
Posts: 20
Location: SOUTH AFRICA

Posted: Tue Jun 02, 2015 9:10 am Post subject: 912 rough running below 3000 rpm

Thanks for that Guy, if I don't solve this by other means then fortunately

the wing tanks can come out.

Flynn



--

Roger Lee

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

Posted: Tue Jun 02, 2015 3:47 pm Post subject: Re: 912 rough running below 3000 rpm

Hi Flynn,



This isn't the ignition modules, wrong symptoms. This is either fuel or the gearbox. The carbs are clean and nothing is in the mixture jet (corner of the float bowl) or the idle jet?  I take it the idle is in sync and it isn't set too low an rpm? If the gearbox is a little on the loose side it could need a re-shim. This can be intermittent due to load changes when there is an rpm change.  Have the float armatures that the float push up on been set to the proper height of 10.5mm from the edge of the carb to the top of the float armature? (You may have a tad bit of flooding). Could the floats themselves be a little heavy causing some mild flooding?

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

flynn elliott

Joined: 23 Jun 2007
Posts: 20
Location: SOUTH AFRICA

Posted: Wed Jun 03, 2015 12:39 am Post subject: 912 rough running below 3000 rpm

Thanks Roger, would you clarify exactly where to measure 10.5mm. i.e

armatures up or down and what area of edge of carb.

Thanks



--

Roger Lee

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

Posted: Wed Jun 03, 2015 6:00 am Post subject: Re: 912 rough running below 3000 rpm

Hi Flynn,



The carb must be off the engine and held upside down. Take a MM ruler and stand it upright (straight up) on the outside lip of the carb. Now slide it over towards the float armature so you can see the ruler marks next to the float armature. The top of the float armature should be 10.5mm. If it is not just bend the tab where the float needle is suspended to obtain the proper 10.5mm height. This is what controls the fuel level in the bowl as the floats push up against it. If it is off adjustment it can cause some flooding and rough running.

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

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