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Engine run on when trying to stop.

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Thumper

Joined: 24 Aug 2008
Posts: 46
Location: Oakland TN.

Posted: Wed Jul 03, 2013 6:42 am Post subject: Engine run on when trying to stop.

I am putting this out there mostly for Roger but chime in as needed.  Rotax 912ULS almost 800 hours on engine. 



Problem: Engine will continue to run diesel mode when I kill the mag switches when the engine is hot.



Symptoms: I have tried one mag at a time, adding a little throttle before turning them off, cooling the engine with a long low power decent, Idle speed is 1800-2000rpm, changed antifreeze, replaced carb balance crossover tube (found a hole), changed spark plugs, checked wires for any pulled out of connectors, grounds are all tight on the top of engine where coils are mounted......



History.  No problems last summer. This year the problem started after returning from Sun-N-Fun but it is not even real hot yet here in W TN.  I have been running a lot of 100LL in the past year as I fly 30-50 hours a month and need fuel to get home.  At first it was intermittent now about 80% of the time.  Tried changing spark plugs, drained fuel and now only have 93 pump gas with alcohol, did find a hole in the carb balance tube and repaired it, sometimes the only way to get it to stop is turn off the fuel valve.  If it is dieseling I can advance the throttle and it speeds up.  On warm up and run up I do get the proper 120-150 RPM drop when doing a mag check.  I did a good mechanical carb balance by the book before leaving for Sun-N-Fun and then had the carbs vacuum balance checked by Lockwood when in Florida and they said it could not be any better, but I was not having the problem then.  I did watch the online fuels webinar and did not always run the engine above 5000 as they recommended on 100LL.  But I do now.



Any help Roger or others can give me I will take.  This has to be hard on my engine.



Thanks ahead of time for the help.

Dennis Long

_________________
Dennis Long
Oakland TN
2000 Aeroprakt A20 Vista Cruiser, 2016 A22LS Aeroprakt
Previously Kolb Mark IIIC, 94 Firestar, 84 Ultrastar.
1200+hours since 1/1/2009

rickofudall

Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA

Posted: Wed Jul 03, 2013 7:28 am Post subject: Engine run on when trying to stop.

Dennis, I always recommend doing the cheap things first1. Check you mag switch grounds. If you have a key switch like a Cessna, add a dedicated ground. If you can get out the switch easily try grounding the switches when the engine is in diesel mode IF AND ONLY IF it can be done safely.

 2. If you have toggle switches for your mags, check to make sure they have not failed internally. Even if you have to replace them to test, you're looking at $10 for a couple at Rat Shack.

 Rick Girard



On Wed, Jul 3, 2013 at 9:42 AM, Thumper <dlong1957(at)yahoo.com (dlong1957(at)yahoo.com)> wrote:

  	  Quote: 	
		  --> RotaxEngines-List message posted by: "Thumper" <dlong1957(at)yahoo.com (dlong1957(at)yahoo.com)>

  

 I am putting this out there mostly for Roger but chime in as needed.  Rotax 912ULS almost 800 hours on engine.

 

 Problem: Engine will continue to run diesel mode when I kill the mag switches when the engine is hot.

 

 Symptoms: I have tried one mag at a time, adding a little throttle before turning them off, cooling the engine with a long low power decent, Idle speed is 1800-2000rpm, changed antifreeze, replaced carb balance crossover tube (found a hole), changed spark plugs, checked wires for any pulled out of connectors, grounds are all tight on the top of engine where coils are mounted......

  

 History.  No problems last summer. This year the problem started after returning from Sun-N-Fun but it is not even real hot yet here in W TN.  I have been running a lot of 100LL in the past year as I fly 30-50 hours a month and need fuel to get home.  At first it was intermittent now about 80% of the time.  Tried changing spark plugs, drained fuel and now only have 93 pump gas with alcohol, did find a hole in the carb balance tube and repaired it, sometimes the only way to get it to stop is turn off the fuel valve.  If it is dieseling I can advance the throttle and it speeds up.  On warm up and run up I do get the proper 120-150 RPM drop when doing a mag check.  I did a good mechanical carb balance by the book before leaving for Sun-N-Fun and then had the carbs vacuum balance checked by Lockwood when in Florida and they said it could not be any better, but I was not having the problem then.  I did watch the online fuels webinar and did not always run the engine above 5000 as!

    they recommended on 100LL.  But I do now.

 

 Any help Roger or others can give me I will take.  This has to be hard on my engine.

 

 Thanks ahead of time for the help.

 Dennis Long

 

 --------

 Dennis Long

 Oakland TN

 2000 Aeroprakt A20 Vista Cruiser

 Previously Kolb Mark IIIC, 94 Firestar, 84 Ultrastar.

 700+hours since 1/1/2009

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=403863#403863

 

 

 

 

 

 

 

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 ="_blank">http://www.matronics.com/contribution

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-- 

Zulu Delta

Mk IIIC

Thanks, Homer GBYM

It isn't necessary to have relatives in Kansas City in order to be unhappy.

   - Groucho Marx

 

  [quote][b]

_________________
The smallest miracle right in front of you is enough to make you happy....

Roger Lee

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

Posted: Wed Jul 03, 2013 12:51 pm Post subject: Re: Engine run on when trying to stop.

This issue can usually be traced back to either a bad or no carb sync or as Rick pointed out the number one cause of dieseling is a bad wire. It may be attached, but not very good. It could as Rick pointed out be a bad switch or a bad wired connection in that link. This is where I would focus my attention first.

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

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Wed Jul 03, 2013 5:47 pm Post subject: Engine run on when trying to stop.

Dennis:



For an engine to run it takes four (4) things:

1 - Fuel

2 - Oxygen

3 - Heat usually in the way of a spark

4 - Correct timing

For an engine to Diesel it takes any one OR more of the following:

 1 - Fuel - YES - Most definitely - BUT, we are not talking about too much fuel or too little fuel - We are saying you must have something to burn for ANY type of combustion to take place.

2 - Oxygen - YES  - Most definitely

 3 - HEAT - And not a SPARK!  Heat as in a HOT SPOT - A glowing carbon spot - A glowing BURR such as a bad spark plug thread hanging into the cylinder - A glowing BURR on the spark plug.

4 - Timing - NO - If the timing was bad you would not have a smooth running engine and your Mag check would be bad.

 My GUESS is go with #3!

Oh!  Mag switch?  Which make and model Mag Switch do you have?  If it is a Bendix with the START position - There is an AD on that switch and it should be checked annually.

 

Barry

On Wed, Jul 3, 2013 at 10:42 AM, Thumper <dlong1957(at)yahoo.com (dlong1957(at)yahoo.com)> wrote:

 [quote]--> RotaxEngines-List message posted by: "Thumper" <dlong1957(at)yahoo.com (dlong1957(at)yahoo.com)>

  

 I am putting this out there mostly for Roger but chime in as needed.  Rotax 912ULS almost 800 hours on engine.

 

 Problem: Engine will continue to run diesel mode when I kill the mag switches when the engine is hot.

 

 Symptoms: I have tried one mag at a time, adding a little throttle before turning them off, cooling the engine with a long low power decent, Idle speed is 1800-2000rpm, changed antifreeze, replaced carb balance crossover tube (found a hole), changed spark plugs, checked wires for any pulled out of connectors, grounds are all tight on the top of engine where coils are mounted......

  

 History.  No problems last summer. This year the problem started after returning from Sun-N-Fun but it is not even real hot yet here in W TN.  I have been running a lot of 100LL in the past year as I fly 30-50 hours a month and need fuel to get home.  At first it was intermittent now about 80% of the time.  Tried changing spark plugs, drained fuel and now only have 93 pump gas with alcohol, did find a hole in the carb balance tube and repaired it, sometimes the only way to get it to stop is turn off the fuel valve.  If it is dieseling I can advance the throttle and it speeds up.  On warm up and run up I do get the proper 120-150 RPM drop when doing a mag check.  I did a good mechanical carb balance by the book before leaving for Sun-N-Fun and then had the carbs vacuum balance checked by Lockwood when in Florida and they said it could not be any better, but I was not having the problem then.  I did watch the online fuels webinar and did not always run the engine above 5000 as!

    they recommended on 100LL.  But I do now.

 

 Any help Roger or others can give me I will take.  This has to be hard on my engine.

 

 Thanks ahead of time for the help.

 Dennis Long

 

 --------

 Dennis Long

 Oakland TN

 2000 Aeroprakt A20 Vista Cruiser

 Previously Kolb Mark IIIC, 94 Firestar, 84 Ultrastar.

 700+hours since 1/1/2009

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=403863#403863

 

 

 

 

 

 

 

 ===========

 -List" target="_blank">http://www.matronics.com/Navigator?RotaxEngines-List

 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 [b]

Dick Maddux

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

Posted: Thu Jul 04, 2013 7:40 am Post subject: Engine run on when trying to stop.

Dennis,

  I have had this problem for about a year (or more) now. I have done  the carbs,gearbox shimming,fuel additives,new plugs,bore scoping cylinders for  carbon deposits,high octane boosters/gas,shut down at higher rpms,gone to a  lighter prop( which helped a little),etc..you name it I have done it ALL to  no avail.( I thought I was the only one in the country with this problem)

  Now when my engine diesels ,it turns backwards about 3-6  revolutions.( my theory is that the prop stops at the peak of the"dogs" in  the gearbox and it flips the prop backwards)  As a result ,I have to  do the valve check to make sure I don't have any air ingestion in the lifters (I  have done it at least a dozen times and can do this check in my sleep now)  I have never found any air, at least according to the tappet clearance  check Rotax specifies. 

 I thought about using Velcro to attach my cowl as it would come off easier  during these checks ! (lol)

 However, I have not had this problem in the last few months because I  have used a different shutdown method and it appears to be working well.

  I now pull the throttle back to about 1500 rpm,shut off one mag then  pull further back to about 1000-1100 rpm then shut off the other mag. This seems  to have solved my problem, even with a warm engine (mine never really gets  hot in my radial nosed Kitfox)

  Prior to this method I would shut down at around 1800 rpm and  then I might get the diseling on occasion.

  I know the gearbox doesn't like low rpm's but you are only there for  a very short time before the engine quits.

  Give this a shot and see if it works for you. 

  Please let us know.

                                            Dick Maddux

                                            912 UL (400 hrs tt)

 [quote][b]

BARRY CHECK 6

Joined: 15 Mar 2011
Posts: 738

Posted: Fri Jul 05, 2013 3:19 am Post subject: Engine run on when trying to stop.

I swear, I have never heard of an engine with more reported issues than the ROTAX.  I was once told: "It is not the engine, it is the operators."  But, even then, shouldn't ROTAX design an engine to be at least somewhat idiot proof? My professor once said:  The only way to make something idiot proof is to remove the idiot.  But, even then - Fifty million Frenchmen can't be wrong!

Barry



 

On Thu, Jul 4, 2013 at 11:36 AM,  <Catz631(at)aol.com (Catz631(at)aol.com)> wrote:

[quote]      Dennis,

  I have had this problem for about a year (or more) now. I have done  the carbs,gearbox shimming,fuel additives,new plugs,bore scoping cylinders for  carbon deposits,high octane boosters/gas,shut down at higher rpms,gone to a  lighter prop( which helped a little),etc..you name it I have done it ALL to  no avail.( I thought I was the only one in the country with this problem)

  Now when my engine diesels ,it turns backwards about 3-6  revolutions.( my theory is that the prop stops at the peak of the"dogs" in  the gearbox and it flips the prop backwards)  As a result ,I have to  do the valve check to make sure I don't have any air ingestion in the lifters (I  have done it at least a dozen times and can do this check in my sleep now)  I have never found any air, at least according to the tappet clearance  check Rotax specifies. 

 I thought about using Velcro to attach my cowl as it would come off easier  during these checks ! (lol)

 However, I have not had this problem in the last few months because I  have used a different shutdown method and it appears to be working well.

  I now pull the throttle back to about 1500 rpm,shut off one mag then  pull further back to about 1000-1100 rpm then shut off the other mag. This seems  to have solved my problem, even with a warm engine (mine never really gets  hot in my radial nosed Kitfox)

  Prior to this method I would shut down at around 1800 rpm and  then I might get the diseling on occasion.

  I know the gearbox doesn't like low rpm's but you are only there for  a very short time before the engine quits.

  Give this a shot and see if it works for you. 

  Please let us know.

                                            Dick Maddux

                                            912 UL (400 hrs tt)



[b]

Alan Carter

Joined: 02 Jul 2012
Posts: 378
Location: Kent, England.

Posted: Fri Jul 05, 2013 2:11 pm Post subject: Re: Engine run on when trying to stop.

Hi Barry.

I tend to agree with you, at Â£28000 to Â£30000 I expect better,

they seem to have got this wonderful reputation, but they are not so wonderful in my opinion for that sort of money, but I guess there's not a lot of choice out there.

Alan

Thumper

Joined: 24 Aug 2008
Posts: 46
Location: Oakland TN.

Posted: Sat Jul 06, 2013 5:04 am Post subject: Re: Engine run on when trying to stop.

Dennis here, ease off on the Rotax bashing please.  It is not a Rotax part that is bad. As time went on a little more I did not have time to check switches or wiring but the right toggle switch now is the culprit.  OR the wiring to it.  Now it does not drop RPM on run up, as of yesterdays 8 hours of flying and multiple stops, or even make the engine run rough.  So now all I have to do is track that down.  Temporarily I just have to hit the primer button once and it stops fine.  My only issues has been trying to stop the engine not make it run, the best problem to have.  50+ hours last month, how about you.  Guess I fly too much, a good problem to have.

Thanks for all of the help, now to find a wiring schematic to guide me on connections.

Thanks a lot flyers.

Dennis in West Tennessee.  

345+ hours since May 5th 2012 on this airplane.

Fly Safe and Fly Often my friends.

_________________
Dennis Long
Oakland TN
2000 Aeroprakt A20 Vista Cruiser, 2016 A22LS Aeroprakt
Previously Kolb Mark IIIC, 94 Firestar, 84 Ultrastar.
1200+hours since 1/1/2009

Roger Lee

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

Posted: Sat Jul 06, 2013 5:25 am Post subject: Re: Engine run on when trying to stop.

Hi Dennis,



Glad it worked out. Usually that type of issue is a wire or the switch. Nice to see someone taking advantage of lots of flight time.

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

Alan Carter

Joined: 02 Jul 2012
Posts: 378
Location: Kent, England.

Posted: Sat Jul 06, 2013 7:02 am Post subject: Re: Engine run on when trying to stop.

50 hours last month, i,m lucky to get 50 a year.

Alan.

Dick Maddux

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

Posted: Sun Jul 07, 2013 6:07 am Post subject: Engine run on when trying to stop.

Dennis,

  Glad you are nailing down your problem. I too replaced the wiring in  my mag switches and the mag switch itself but that didn't cure the problem.  I believe my problem is not the same as yours. In any event my shutdown  procedure seems to be working well so I will live with it. My engine starts and  runs extremely well and I do like it even though I believe I have worked on  it more then any of my Lyc/Cont engines  on the 13 other aircraft I  have owned thru the years. But then they all take work This group is a  life saver for the many problems that crop up. I live in an area that is pretty  devoid of Rotax engines so the knowledge here really helps.

                                                                    Dick Maddux

                                                                    912UL

 [quote][b]

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