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Uneven Mag Drop 912 ULS
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JohnF

Joined: 13 May 2010
Posts: 124

Posted: Thu May 22, 2014 12:07 pm Post subject: Uneven Mag Drop 912 ULS

This looks like a case of "It was working until I fixed it"



Annual condition inspection; new plugs at 0.027-inches, carbmate showed exact balance, Dyna Vibe gave engine smoothness like a turbine, cylinder differential pressure almost perfect all cylinders, began using non-ethanol 91-octane gas, no oil consumption, crossover fittings (hoses) all tight, cruise speed normal, climb out at max throttle 5,000+ then over 5,100 after a few moments while still over the runway.

Spark plug wires firmly attached



"Killing" A side ignition, mag drop averages 150 rpm

"Killing" B side ignition, mag drop averages 290 rpm, so it looks like a

  problem with the A side ignition.



Next try will be new plugs (again) on top of cyl #1 & 2

                       new plugs (again) on bottom of cyl #4 & 3 to eliminate a bad new plug.



Anything else to check?

Roger Lee

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

Posted: Thu May 22, 2014 1:25 pm Post subject: Re: Uneven Mag Drop 912 ULS

What rpm are you doing the mag drop at?

It does sound like a plug or wire.

Plugs are worth checking / replacing and gaps. Since you pulled the plug boots off you may have inadvertently pulled the plug wire a little too much where it goes into the boot. It wouldn't hurt to unscrew each one and trim the wire back 1/4" and then thread the boot back on. 



I even think 150 is a little high if the rpm is 3500 and under. Average is 50-100.

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

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Thu May 22, 2014 2:21 pm Post subject: Re: Uneven Mag Drop 912 ULS

Roger,



I run up to 4,000 rpm and then 'kill' each circuit in turn.



I have never 'unscrewed' a plug boot...I assume I can hold the main wire and twist on the 'plug' end that would connect to the top of the spark plug. I am  picking up 4 new plugs tomorrow and will gap and install...will try that plug wire trimming and reattaching.



Thanks for the input Roger...I wish you were a bit closer, I would just fly down to Tuscon and  put the whole thing into your hands !



John

henryroden

Joined: 09 Jan 2006
Posts: 13
Location: Albuquerque

Posted: Fri May 23, 2014 12:28 am Post subject: Re: Uneven Mag Drop 912 ULS

John,

       I had almost the exact same problem except the mag drop was about 350 rpm on one side when checked at 4,000 rpm. What I found was that I had switched the two top left plug wires. #2 went to #4 plug & #4 went to #2 plug. The surprise was that it ran as well as it did with the plug wires reversed. Some idiot (me) had mismarked the cylinders when pulling the wires off.

Henry

max8992

Joined: 28 Jul 2011
Posts: 142

Posted: Fri May 23, 2014 2:04 am Post subject: Uneven Mag Drop 912 ULS

Hi There All,



Did the same as the length of the wire pushed me to switch them. On two mags

at least all cylinders are lighted at the right time, but with one mag one

cylinder is not lighted at the right time...



Max  Cointe

mcointe(at)free.fr

F-PMLH Europa XS_TriGear

Kit #560-2003 912ULS/AirmasterAP332 490 hours



F-PLDJ Dyn’Aéro MCR 4S 

Kit #27-2002 912ULSFR/MTProp MTV7A 1600 heures

-----Message d'origine-----

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[mailto:owner-rotaxengines-list-server(at)matronics.com] De la part de

krazydoc33

Envoyé : vendredi 23 mai 2014 10:29

À : rotaxengines-list(at)matronics.com

Objet : Re: Uneven Mag Drop 912 ULS




--> <galaxyone(at)juno.com>



John,

       I had almost the exact same problem except the mag drop was about 350

rpm on one side when checked at 4,000 rpm. What I found was that I had

switched the two top left plug wires. #2 went to #4 plug & #4 went to #2

plug. The surprise was that it ran as well as it did with the plug wires

reversed. Some idiot (me) had mismarked the cylinders when pulling the wires

off.

Henry





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=423628#423628

_________________
Max8992
Europa XS #560 F-PMLH

Dick Maddux

Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl

Posted: Fri May 23, 2014 4:43 am Post subject: Uneven Mag Drop 912 ULS

John,

  I had a similar problem one time so I walked down the airport with my new plugs to a friends hanger. He had a spark plug "bomb" checker as part of his Champion spark plug cleaner unit. We checked the new plugs and sure enough, one of them would not fire under air pressure. I threw that one in the bin checked another and soon I was "back in business." So, you might have a bad "new" plug.

                                                      Dick Maddux

                                                      912 UL

 [quote][b]

Roger Lee

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

Posted: Fri May 23, 2014 11:11 am Post subject: Re: Uneven Mag Drop 912 ULS

plugs can be bad out of the box. I have had two over the years.

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

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Fri May 23, 2014 11:29 am Post subject: Re: Uneven Mag Drop 912 ULS

I found all plugs on the A side very black and sooty. Had perhaps 3 or 4 hours total running time on them.



I trimmed the spark plug wires back 1/4-inch and reinstalled the boots, and made absolutely certain the boots were correctly and well seated on the new spark plugs that I just purchased and set to 0.027.



Have not yet run the engine..my time at the airport is very limited because I am a care taker for my invalid wife, and I can only 'get away' for a few hours at a time...tomorrow I hope to run the plane and see if I made any progress.



I appreciate the help I have been give more than you might expect. 



John

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Sat May 24, 2014 9:16 am Post subject: Re: Uneven Mag Drop 912 ULS

The mystery deepens



I ran the engine after new plugs on the A side and now the problem has shifted to the B side.



I was getting too much rpm drop when the B side was turned off, now the excessive rpm drop occurs when the A side is turned off.



First mag drop checks at 3500 showed 70 rpm drop running with the B side only operating, and 170 rpm drop when the A side only was operating.



Then at 4,000 rpm the first mag checks showed a rpm drop of 160 and 130 on A and B side. I thought it was fixed...but....



Subsequent mag checks consistently showed the when the A side was killed the rpm dropped an average of 385 rpm (4 tries), and when the B side was killed the average of 4 tries showed a drop of 120 rpm.



This switching of excessive mag drop from the A side to the B side seems

to indicate some sort of bad connection or other intermittent fault.



Its interesting to note that the first tries showed normal and acceptable rpm drops as the mags were 'killed' but subsequent tries showed bad drops on the opposite side from yesterday's trials.



I am really confused now.

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Sat May 24, 2014 12:37 pm Post subject: Re: Uneven Mag Drop 912 ULS

I have been really thinking about this problem, and recalled that two years ago I had a situation where I was getting serious rpm drops during mag checks. A local A&P and an experienced RV builder were helping me. We noticed that if the top cowling was off everything was fine. When fully assembled with the top cowling back on, the mag drop was seriously down again.



I found an exhaust pipe slightly out of the 'socket' on the muffler. When fully cowled the engine was 'sucking' up exhaust fumes, and naturally the engine didn't work well. With the top cowling off there was plenty of free air and the engine worked fine.



I am going to pull the cowling again and closely inspect for possible exhaust leaks.



Anything else you can suggest?

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Sun May 25, 2014 12:50 pm Post subject: Re: Uneven Mag Drop 912 ULS

My hope of finding a easy fix to my mag drop problem faded when no exhaust leaks were found.. bad mag drop with or without cowling on/off.



Next effort will be to recheck carb balance in case that somehow got screwed up. ('tho I don't really expect this is the problem, but everything I can think of needs to be done !)



Problem was on A side ignition, then switched to B side, and is staying on the B side being the problem. Problem exists if mag run up is done at 3500 or 4000, and same results if reading an MGL tach I have installed instead of the Dynon D-180's tach.)



Failing in this, I guess the only thing left to try is to replace plugs and trim plug wires a bit on the remaining 4 plugs on which I have not done this.



/John

Dick Maddux

Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl

Posted: Mon May 26, 2014 4:42 am Post subject: Uneven Mag Drop 912 ULS

I doubt seriously your uneven mag drop is caused by your carbs. It most likely is an ignition problem. I have dealt with similar problems with my old (mid 90's) 912 UL. 

 During my last event I "bit the bullet" and bought new ignition wires and caps when I was having bad mag drops. This cured the problem. Now in my case the wires/caps were old and probably needed replacement anyway so I didn't feel too bad about it. I was able to save on the wire /plugs thru online vendors.

  I think if you clip the wires or search out a bad plug (bomb check them),you will find your problem.

  My opinion

                       Dick Maddux

                       Fox 4

                       912UL

 [quote][b]

Roger Lee

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

Posted: Mon May 26, 2014 5:04 am Post subject: Re: Uneven Mag Drop 912 ULS

All wires should have been trimmed. All plug gaps re-checked. I would do both of these first. 

Black sooty plugs under 3500 rpm can be very normal and can move to different plugs at times and is different for every engine.

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

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Mon May 26, 2014 5:11 am Post subject: Uneven Mag Drop 912 ULS

Dick,

  

 I agree with you. The carbs are not likely to be my mag drop problem. Prior  to a lot of work during the annual condx inspection things were fine. Something  I probably did is causing my problem, and I am at a loss for what it might be,  so I am going back over everything I did to try to eliminate any remote  possibility. Thanks for your input.

  

 John

  	  Quote: 	
		     ----- Origin.al Message ----- 

   From:    Catz631(at)aol.com (Catz631(at)aol.com)    

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

   Sent: Monday, May 26, 2014 6:40 AM

   Subject: Re: Uneven    Mag Drop 912 ULS

   



   I doubt seriously your uneven mag drop is caused by your carbs. It most    likely is an ignition problem. I have dealt with similar problems with my old    (mid 90's) 912 UL. 

   During my last event I "bit the bullet" and bought new ignition wires and    caps when I was having bad mag drops. This cured the problem. Now in my case    the wires/caps were old and probably needed replacement anyway so I didn't    feel too bad about it. I was able to save on the wire /plugs thru online    vendors.

    I think if you clip the wires or search out a bad plug (bomb check    them),you will find your problem.

    My opinion

                            Dick Maddux

                            Fox 4

                            912UL

 	  Quote: 	
		  



ist">http://www.matronics.com/Navigator?RotaxEngines-List

ics.com

.matronics.com/contribution



	
	
    	 		 			 				 			 		 		 			

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JohnF

Joined: 13 May 2010
Posts: 124

Posted: Mon May 26, 2014 5:16 am Post subject: Re: Uneven Mag Drop 912 ULS

Thanks, Roger...have trimmed the A side, and doing the B side this morning and going over the carb balance even tho I doubt it is involved, but the mag drop was OK prior to a lot of work during the annual condx inspection, so I have to think it was something I did.



I still may have to fly to Tuscon and drop it into your hands !!!

John

thekelleygroup(at)msn.com
Guest

Posted: Mon May 26, 2014 5:24 am Post subject: Uneven Mag Drop 912 ULS

Please remove me for this list!!!



Sent from my iPhone



On May 26, 2014, at 8:21 AM, "JohnF" <n29cx(at)ridgeviewtel.us (n29cx(at)ridgeviewtel.us)> wrote:

[quote]       Dick,

  

 I agree with you. The carbs are not likely to be my mag drop problem. Prior  to a lot of work during the annual condx inspection things were fine. Something  I probably did is causing my problem, and I am at a loss for what it might be,  so I am going back over everything I did to try to eliminate any remote  possibility. Thanks for your input.

  

 John

  	  Quote: 	
		     ----- Origin.al Message ----- 

   From:    Catz631(at)aol.com (Catz631(at)aol.com)    

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

   Sent: Monday, May 26, 2014 6:40 AM

   Subject: Re: Uneven    Mag Drop 912 ULS

   



   I doubt seriously your uneven mag drop is caused by your carbs. It most    likely is an ignition problem. I have dealt with similar problems with my old    (mid 90's) 912 UL. 

   During my last event I "bit the bullet" and bought new ignition wires and    caps when I was having bad mag drops. This cured the problem. Now in my case    the wires/caps were old and probably needed replacement anyway so I didn't    feel too bad about it. I was able to save on the wire /plugs thru online    vendors.

    I think if you clip the wires or search out a bad plug (bomb check    them),you will find your problem.

    My opinion

                            Dick Maddux

                            Fox 4

                            912UL

 	  Quote: 	
		  



ist">http://www.matronics.com/Navigator?RotaxEngines-List

ics.com

.matronics.com/contribution



	
	
 



   	 		 			 				 			 		 		 			

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[b]

peteohms

Joined: 31 Oct 2007
Posts: 224
Location: Leander, TX

Posted: Mon May 26, 2014 6:01 am Post subject: Uneven Mag Drop 912 ULS

Kelly, Go here.



http://www.matronics.com/subscription/





On May 26, 2014, at 8:23 AM, Richard Kelley <thekelleygroup(at)msn.com (thekelleygroup(at)msn.com)> wrote:

[quote]Please remove me for this list!!!



Sent from my iPhone



On May 26, 2014, at 8:21 AM, "JohnF" <n29cx(at)ridgeviewtel.us (n29cx(at)ridgeviewtel.us)> wrote:

 	  Quote: 	
		         Dick,

  

 I agree with you. The carbs are not likely to be my mag drop problem. Prior  to a lot of work during the annual condx inspection things were fine. Something  I probably did is causing my problem, and I am at a loss for what it might be,  so I am going back over everything I did to try to eliminate any remote  possibility. Thanks for your input.

  

 John

  	  Quote: 	
		     ----- Origin.al Message ----- 

   From:    Catz631(at)aol.com (Catz631(at)aol.com)    

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

   Sent: Monday, May 26, 2014 6:40 AM

   Subject: Re: Uneven    Mag Drop 912 ULS

   



   I doubt seriously your uneven mag drop is caused by your carbs. It most    likely is an ignition problem. I have dealt with similar problems with my old    (mid 90's) 912 UL. 

   During my last event I "bit the bullet" and bought new ignition wires and    caps when I was having bad mag drops. This cured the problem. Now in my case    the wires/caps were old and probably needed replacement anyway so I didn't    feel too bad about it. I was able to save on the wire /plugs thru online    vendors.

    I think if you clip the wires or search out a bad plug (bomb check    them),you will find your problem.

    My opinion

                            Dick Maddux

                            Fox 4

                            912UL

 	  Quote: 	
		  



ist">http://www.matronics.com/Navigator?RotaxEngines-List

ics.com

.matronics.com/contribution



	
	
 



   	 		 			 				 			 		 		 			

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[b]

_________________
Pete
Leander, TX
Kitfox III, 912ul, Grove

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Mon May 26, 2014 9:15 am Post subject: Uneven Mag Drop 912 ULS

John,



Easy ways just don't work!  Well, they do, but only for those people that won the lottery.   



In simple terms, even if you had a exhaust leak, it very we'll Would Not give you  a

 Mag drop.  Nor would an 

out of tune Carb.  Nor would the point of running With or Without the cowling on.  That logic would follow checking the air pressure in your tires for the Mag drop!

  IF the Mag drop was good on one Mag, you are STILL using the SAME Carb for the Good Mag as for the Bad Mag, no reason why it would change for the second Mag

 ..  Do ya see the logic there?

Next is the Exhaust System.  If there was an Exhaust leak, it would depend where the leak was...  An exhaust valve leak would leak on either Mag so No difference in Mag check 

 with this scenario.  If it was a pipe or muffler leaking  it would again be the same leak no matter which Mag you were on, 

 so No difference in Mag check 

with this scenario either.  



 This is the way you go about checking out a Mag Drop Problem:



1 - Clean the plugs.

 

2 - TRIPLE check the Timing.



3 - Check the condition AND resistance of the spark plug wires.

 

4 - Did you ever DROP a spark plug?  If so - Replace it, don't think about it, do it.  OR, test it on a Pressure-Voltage Spark Plug checking station. Those are your ONLY options when it come to plugs.

 

5 - This is a bit more difficult - Check the Voltage coming out of your Mag.  You will need a High Voltage Probe Volt Meter, not many people have them.

 

6 - Question:  Do you get a Mag drop at BOTH low RPM and high RPM?  If so, then go back to #1 and run through the steps...  1 thru 5.  If it only happens at High RPM then there could be a voltage breakdown of a component and an overhaul is needed.  Problem being - You have a Rotax and both Low and High are both High when you consider the small delta between the two ranges.  SO...  What Next?  SWAP out the Mag with one of known GOOD working condition.

 



These are your options.  Go through the steps and I'm positive you will find the problem.

 



Barry

 

 

 



 

On Sunday, May 25, 2014, JohnF <n29cx(at)ridgeviewtel.us (n29cx(at)ridgeviewtel.us)> wrote:

[quote]  --> RotaxEngines-List message posted by: "JohnF" <n29cx(at)ridgeviewtel.us>

 

 My hope of finding a easy fix to my mag drop problem faded when no exhaust leaks were found.. bad mag drop with or without cowling on/off.

 

 Next effort will be to recheck carb balance in case that somehow got screwed up. ('tho I don't really expect this is the problem, but everything I can think of needs to be done !)

 

 Problem was on A side ignition, then switched to B side, and is staying on the B side being the problem. Problem exists if mag run up is done at 3500 or 4000, and same results if reading an MGL tach I have installed instead of the Dynon D-180's tach.)

   

 Failing in this, I guess the only thing left to try is to replace plugs and trim plug wires a bit on the remaining 4 plugs on which I have not done this.

 

 /John

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=423779#423779

 

 

 

 

 

 

 

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 [b]

wdaniell.longport(at)gmai
Guest

Posted: Mon May 26, 2014 9:44 am Post subject: Uneven Mag Drop 912 ULS

John

I had a similar problem, it was a bad connection in the bundle of wires that sits on top of the engine

 Will



William Daniell



LONGPORT

+57 310 295 0744

  



On Mon, May 26, 2014 at 8:11 AM, JohnF <n29cx(at)ridgeviewtel.us (n29cx(at)ridgeviewtel.us)> wrote:

[quote]        Dick,

 Â 

 I agree with you. The carbs are not likely to be my mag drop problem. Prior  to a lot of work during the annual condx inspection things were fine. Something  I probably did is causing my problem, and I am at a loss for what it might be,  so I am going back over everything I did to try to eliminate any remote  possibility. Thanks for your input.

 Â 

 John

  	  Quote: 	
		     ----- Origin.al Message ----- 

   From:    Catz631(at)aol.com (Catz631(at)aol.com)    

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

   Sent: Monday, May 26, 2014 6:40 AM

   Subject: Re: Uneven    Mag Drop 912 ULS

   



   I doubt seriously your uneven mag drop is caused by your carbs. It most    likely is an ignition problem. I have dealt with similar problems with my old    (mid 90's) 912 UL. 

   During my last event I "bit the bullet" and bought new ignition wires and    caps when I was having bad mag drops. This cured the problem. Now in my case    the wires/caps were old and probably needed replacement anyway so I didn't    feel too bad about it. I was able to save on the wire /plugs thru online    vendors.

   Â I think if you clip the wires or search out a bad plug (bomb check    them),you will find your problem.

   Â My opinion

   Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â     Dick Maddux

   Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â     Fox 4

   Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â     912UL

 	  Quote: 	
		  



ist">http://www.matronics.com/Navigator?RotaxEngines-List

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[b]

JohnF

Joined: 13 May 2010
Posts: 124

Posted: Mon May 26, 2014 10:07 am Post subject: Re: Uneven Mag Drop 912 ULS

Progress on the mag drop !



Taking suggestions from you folks,  I  trimmed back the plug wires on the ignition side that I had not yet done. 



As expected, mag balance was perfect.



As to exhaust leak...prior experience has shown me that a serious leak, one pipe 1/2 way out of the 'socket' on the muffler...definitely and repeatedly showed that mag drop was OK with the top cowling off, but bad with it one. An A&P and an experienced builder working with me saw this at least three times before I figured out what the problem was. Fixing the exhaust pipe into the muffler fixed everything.



As to today....the mag drop, average of 10 'runs' is now only 14 rpm difference between A and B sides. I still am not happy with the drop, its 227 rpm drop on A side, and 241 rpm drop on B side. I have buttoned up the cowling and will fly tomorrow, weather permitting, and run the plane hard for about 30 minutes and see if that changes anything.



My guess now is that the wire into the boot on cyl #4, bottom, was too far back in;  trimming it as Roger and others suggested fixed the large difference in mag drops.



My appreciation for all the help.



John

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