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Rotax 912 ULS Mystery

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JohnF

Joined: 13 May 2010
Posts: 124

Posted: Fri Jun 08, 2012 12:23 pm Post subject: Rotax 912 ULS Mystery

Yes, plugs and wires checked and re-checked...all  tags are on correct cylinder. Even if they were not, I can't figure out how it  would work just fine sometimes and sometimes not...wires to plugs wouldn't jump  around by thermselves.

  

 As to fuel hoses...no auto stuff...alll fuel hoses  are Rotax supplied lines; nothing kinked.

  

 The salient thing here is the movement from normal  operation to abnormal operation for an unknown reason. I know there's a reason,  I just don't know what it is ! ! 

  

 86.4 hours on the engine.

  

 PLEASE continue coming with ideas/suggestions no  matter how 'far out' --  we're really at sea on this one.

  

 John

  

  

   [quote][b]

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BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Fri Jun 08, 2012 1:29 pm Post subject: Rotax 912 ULS Mystery

John:



Questions come to mind:

Was the engine overhauled?
Is the engine Factory New?
Did you check the service bulletin on the fuel pump fuel line?
Have you done a compression check?  
Have you pulled the spark plugs immediately after the problem occurs?
Have you done a high voltage check on the spark plug wires for breakdown?
Since after the long taxi the problem occurs - Are you using AvGas? 
Since after the long taxi the problem occurs - Are you seeing plug fouling?
Since after the long taxi the problem occurs - What color are the deposits on the exhaust pipe?
Vibration causes many a problem - You have the problem then you dismantle the cowling and look under the hood - Then the engine runs good - You shut down for the day - You re-assemble the cowling and ALL the items you touched - Then the next day the problem reoccurs - And if I have read correctly this is the procedure that you have followed and each time the problem came back?  Sure points to something that is being moved and touched. 
Where is the ignition system mounted?  Mounting coils on the engine is not a good practice.  Mounting near heat is not a good practice. OK - That is all I can think of right now.  



 Good Luck,

Barry

  [quote][b]

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JohnF

Joined: 13 May 2010
Posts: 124

Posted: Fri Jun 08, 2012 2:06 pm Post subject: Rotax 912 ULS Mystery

Barry, here are the answers to your  questions.

  

 1. Not overhauled

 2. Factory new 86.4 hours total time

 3. Service bulletin re pump hoses not applicable. I  have just installed the new style fuel pump...after problems, reinstalled the  old one...no help, put back on the new pump

 4. Compression check? Yes..all cylinders within a  psi of each other and all like factory new readings

 5. Pulled plugs after problems? Yes, the first  time, and regapped them from 0.023 to 0.027 per a suggestion from Roger Lee who  is a real Rotax guru

 6. Av gas"? NO 91octane auto fuel  always been  used...only once did I add 5-gallons of 100LL but that was some time ago when wx  kept plane down longer than I wanted with autogas in it

 7.Fouling? Yes...the problem is engine running WAY  WAY too rich when it is acting up....brand new plugs, properly installed . 10  minutes of running blackened them 

 8. Exhaust deposts...No  

 9. Ignition location? This one thing I really  dislike about the Rotax; if you want to really get involved with the timing, and  ignition you probably will have to remove the engine entirely 

     Most of it is really buried  beneath the myrid number of hoses....really difficult machine to service if what  you need isn't right on the top of the machine.

 Thanks for your input

 John

  

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BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Fri Jun 08, 2012 2:58 pm Post subject: Rotax 912 ULS Mystery

John:



I inserted my response within the body of the email.

Barry



On Fri, Jun 8, 2012 at 6:05 PM, JohnF <n29cx(at)ridgeviewtel.us (n29cx(at)ridgeviewtel.us)> wrote:

  	  Quote: 	
		         Barry, here are the answers to your  questions.

  

 1. Not overhauled

 2. Factory new 86.4 hours total time

 3. Service bulletin re pump hoses not applicable. I  have just installed the new style fuel pump...after problems, reinstalled the  old one...no help, put back on the new pump

 4. Compression check? Yes..all cylinders within a  psi of each other and all like factory new readings

 5. Pulled plugs after problems? Yes, the first  time, and regapped them from 0.023 to 0.027 per a suggestion from Roger Lee who  is a real Rotax guru

 6. Av gas"? NO 91octane auto fuel  always been  used...only once did I add 5-gallons of 100LL but that was some time ago when wx  kept plane down longer than I wanted with autogas in it

 7.Fouling? Yes...the problem is engine running WAY  WAY too rich when it is acting up....brand new plugs, properly installed .. 10  minutes of running blackened them



	
[Barry] - That is a BINGO - Since they are becoming black that points to a couple possibles: 

a> Engine set too rich for both the idle and high end.  

 b> Poor Spark 

c> Opening the plug gap may help a little but a difference of 0.004" is not going to cure the problem.  

d> BLACK is an indication of two things - Carbon from too rich a fuel mixture and OIL!

 Oil is a bad thing because it could indicate bad rings or the rings were installed incorrectly.

Rich Fuel - Is not a problem since that can be adjusted via the carb.

QUESTION:  Any idea what kind of voltage the ignition system is producing?  

 GA Mags put out about 18,000 Volts,  Electronic Ignitions are 60,000 to 100,000 Volts and the gaps on them are 0.035 to 0.045".  Big gaps equal big sparks which equal better fuel burn, more HP and no carbon.

 



QUESTION:  What heat range plugs are you using?  Higher heat range offers less carbon-ing.  BUT, you don't want too high otherwise you can get a hot running engine and maybe pre-ignition.

  

 	  Quote: 	
		   

 8. Exhaust deposts...No  



	
[Barry] - This does not sound correct.  If the plugs are carbon-ing up the rest of the carbon has to be going out the exhaust.  Wipe down the exhaust pipe and see what builds up - Also inspect the rag after wiping. 

 



John - What are your thoughts on my item #10?

QUESTION - Do you have access to an exhaust gas analyzer?  I am in NJ and have a portable one.  

A THOUGHT:  As I mentioned - Heat on an ignition coil can cause problems, indicate a cracked coil and even cause the coil to break down.  Put is a small SCAT Tube and have it blow outside air on the coils.  This is something we do for GA Mags, they run HOT.

 



So, back to you John - Let's solve this issue.

Barry

[quote]  9. Ignition location? This one thing I really  dislike about the Rotax; if you want to really get involved with the timing, and  ignition you probably will have to remove the engine entirely 

     Most of it is really buried  beneath the myrid number of hoses....really difficult machine to service if what  you need isn't right on the top of the machine.

 Thanks for your input

 John

  

 [quote]   ---

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KeysFox

Joined: 05 Jan 2009
Posts: 137

Posted: Fri Jun 08, 2012 4:57 pm Post subject: Rotax 912 ULS Mystery

One of the Rotax gurus might shed some light on carburetor problem that

might cause these symptoms.



However, If plugs on both sides look dark from over rich operation it

seems unlikely that both carbs would act up at the same time unless maybe

there is a cross over tube issue.



I am out of my knowledege zone here so don't take these comments too

seriously



good luck



BJ

Kitfox IV early 912



[quote] Barry, here are the answers to your questions.



 1. Not overhauled

 2. Factory new 86.4 hours total time

 3. Service bulletin re pump hoses not applicable. I have just installed

 the new style fuel pump...after problems, reinstalled the old one...no

 help, put back on the new pump

 4. Compression check? Yes..all cylinders within a psi of each other and

 all like factory new readings

 5. Pulled plugs after problems? Yes, the first time, and regapped them

 from 0.023 to 0.027 per a suggestion from Roger Lee who is a real Rotax

 guru

 6. Av gas"? NO 91octane auto fuel  always been used...only once did I add

 5-gallons of 100LL but that was some time ago when wx kept plane down

 longer than I wanted with autogas in it

 7.Fouling? Yes...the problem is engine running WAY WAY too rich when it is

 acting up....brand new plugs, properly installed .. 10 minutes of running

 blackened them

 8. Exhaust deposts...No

 9. Ignition location? This one thing I really dislike about the Rotax; if

 you want to really get involved with the timing, and ignition you probably

 will have to remove the engine entirely

     Most of it is really buried beneath the myrid number of

 hoses....really difficult machine to service if what you need isn't

 right on the top of the machine.

 Thanks for your input

 John



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B Jones
N154K
443-480-1023

Thom Riddle

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

Posted: Sat Jun 09, 2012 3:49 am Post subject: Re: Rotax 912 ULS Mystery

Several years ago when I was flying an Allegro 2000 (factory built), after several hundred hours on the engine, one cylinder started showing black plugs while the rest were normal.The cylinder was firing ok, in the sense that there was no noticeable power loss or roughness. It did not have the running problems you are having but the mystery of the back plugs (both) on one cylinder made no sense to me. 



I went through everything one would expect to for diagnosing this without a fix until I visually traced out all the tiny little wires in the ingition system and found one little white wire that was almost broken, i.e., the insulation was open and several (but not all) strands of wire broken. I repaired that wire and the black plug syndrome went away. I am not sure which of the wires it was and after hours of studying the ignition wiring diagram I still could not figure out how a single wire could cause this problem on both plugs in one cylinder. And yet repairing that one wire did the trick.



Can't say if this will help in your case but when all else fails, it could be worth the effort to do what I did.

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_________________
Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
- Anonymous

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Sat Jun 09, 2012 4:12 am Post subject: Rotax 912 ULS Mystery

Experience is what you get when you don't get it right the first time.Barry

John & Tom:

As I mentioned check the voltage on the wires.  I just had the problem with an O-235 where all plugs were clean and gaped but the Mag check was intermittent... Sometimes good, sometimes bad.  Pulled the plugs again and there it was hanging in front of me.  The 'cigarette' insulator was cracked and with a slight pull the wire cracked and pulled away.  

 

Everything keeps pointing full circle back to vibration and heat.

Barry

On Sat, Jun 9, 2012 at 7:49 AM, Thom Riddle <riddletr(at)gmail.com (riddletr(at)gmail.com)> wrote:

 [quote]--> RotaxEngines-List message posted by: "Thom Riddle" <riddletr(at)gmail.com (riddletr(at)gmail.com)>

  

 Several years ago when I was flying an Allegro 2000 (factory built), after several hundred hours on the engine, one cylinder started showing black plugs while the rest were normal.The cylinder was firing ok, in the sense that there was no noticeable power loss or roughness. It did not have the running problems you are having but the mystery of the back plugs (both) on one cylinder made no sense to me.

  

 I went through everything one would expect to for diagnosing this without a fix until I visually traced out all the tiny little wires in the ingition system and found one little white wire that was almost broken, i.e., the insulation was open and several (but not all) strands of wire broken. I repaired that wire and the black plug syndrome went away. I am not sure which of the wires it was and after hours of studying the ignition wiring diagram I still could not figure out how a single wire could cause this problem on both plugs in one cylinder. And yet repairing that one wire did the trick.

  

 Can't say if this will help in your case but when all else fails, it could be worth the effort to do what I did.

 

 --------

 Thom Riddle

 Buffalo, NY (9G0)

 Kolb Slingshot SS-021

 Jabiru 2200A #1574

 Tennessee Prop 64x32

 

 Truth is what stands the test of experience.

 - Albert Einstein

 

 

 

 

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JohnF

Joined: 13 May 2010
Posts: 124

Posted: Sat Jun 09, 2012 4:18 am Post subject: Rotax 912 ULS Mystery

Thanks for your help, Thom. I guess that I don;t really like the Rotax 

because it is so darn

hard to get at anything. As configured in the RV-12 most of the ignition 

system is so burried that you probably would have to remove the engine 

completely to get at everything. I would really rather have a Lycoming, but 

I am stuck with the Rotax.



I appreciatie your help. Thank you



John

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