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joeing701(at)simnet.is
Guest

Posted: Sun Jun 17, 2012 5:21 am Post subject: Rotax 912 ul engine problems

Hello list members.



We really need your  expert help regarding a Rotax 912 ul 80 hp engine  

problem my friend has been dealing with for the past  three years or  

ever since he bought the plane.



My friend bought this  Kitfox II aprox. 1990 model from USA and has  

been trying to solve a rough running engine problem, and is about to  

give up on the project.



Here is the symptoms:



Engine starts perfectly and runs on both mags with a drop within 100  

rpm. When airborne the rough running starts around 3500-4500.  

Everything shakes very violently and aircraft looses altitude. Most  

often you can give it full power to continue flying, but when power is  

reduced, the shaking starts again.



What has been done:



All fuel system has been checked, cleaned many times. Fuel pump  

replaced, including electrical pump added. Carbs have been cleaned,  

all jets replaced with new, new throttle cable. See here:

http://www.chiefaircraft.com/aircraft/fuel-systems-carbs/throttle-cables-rotax/ma-mct100d048.html



Everything has been adjusted and calibrated according to Rotax  

manual.  The mid range was suspected so we have tried to fine tune the  

jet needle by adjusting the clip, but does not seem to change anything.

So we have almost ruled out fuel problems and are beginning to suspect  

the ignition system. Most likely the trigger system because the mag  

drop is within the normal drop, i.e. 90-100 rpm.

The running of the engine does not seem to change after it warms up,  

so the coils do not seem to be the problem.

All wires have been checked and inspected.

The engine sat for some time in a unheated trailer, before my friend  

bought the plane. He did clean the triggers of rust which had formed  

on the metal part.

The triggers are really hard to reach on the Kitfox due to tight space  

between the firewall and engine.

The engine will need to be removed to do any work on the charging and  

trigger system.

Before we do that, I just wanted to ask you experts if you had any  

other ideas?



Really appreciate any help.



Best regards,

Johann G.

Iceland.

klinefelter.kevin(at)gmai
Guest

Posted: Sun Jun 17, 2012 8:10 am Post subject: Rotax 912 ul engine problems

I believe it is very unlikely that the problem is ignition. Replace the spark plugs with the proper type and gap them properly. Do the pull test on all the plug caps. That should cover the most common ignition problems.

You mention a new throttle cable, and other carb parts. When we're the carbs last rebuilt? If its been several years I would start with having the carbs rebuilt properly. 

It is helpful to know what work was done to the engine immediately before the problem started. 

Kevin



On Jun 17, 2012, at 6:21 AM, JÃ³hann JÃ³hannsson <joeing701(at)simnet.is> wrote:



 	  Quote: 	
		   

 

 Hello list members.

 

 We really need your  expert help regarding a Rotax 912 ul 80 hp engine problem my friend has been dealing with for the past  three years or ever since he bought the plane.

 

 My friend bought this  Kitfox II aprox. 1990 model from USA and has been trying to solve a rough running engine problem, and is about to give up on the project.

 

 Here is the symptoms:

 

 Engine starts perfectly and runs on both mags with a drop within 100 rpm. When airborne the rough running starts around 3500-4500. Everything shakes very violently and aircraft looses altitude. Most often you can give it full power to continue flying, but when power is reduced, the shaking starts again.

 

 What has been done:

 

 All fuel system has been checked, cleaned many times. Fuel pump replaced, including electrical pump added. Carbs have been cleaned, all jets replaced with new, new throttle cable. See here:

 http://www.chiefaircraft.com/aircraft/fuel-systems-carbs/throttle-cables-rotax/ma-mct100d048.html

 

 Everything has been adjusted and calibrated according to Rotax manual.  The mid range was suspected so we have tried to fine tune the jet needle by adjusting the clip, but does not seem to change anything.

 So we have almost ruled out fuel problems and are beginning to suspect the ignition system. Most likely the trigger system because the mag drop is within the normal drop, i.e. 90-100 rpm.

 The running of the engine does not seem to change after it warms up, so the coils do not seem to be the problem.

 All wires have been checked and inspected.

 The engine sat for some time in a unheated trailer, before my friend bought the plane. He did clean the triggers of rust which had formed on the metal part.

 The triggers are really hard to reach on the Kitfox due to tight space between the firewall and engine.

 The engine will need to be removed to do any work on the charging and trigger system.

 Before we do that, I just wanted to ask you experts if you had any other ideas?

 

 Really appreciate any help.

 

 Best regards,

 Johann G.

 Iceland.

fygdog(at)yahoo.com
Guest

Posted: Sun Jun 17, 2012 8:34 am Post subject: Rotax 912 ul engine problems

check that the vent tubes have not been relocated to an improper location



--- On Sun, 6/17/12, klinefelter.kevin(at)gmail.com <klinefelter.kevin(at)gmail.com> wrote:

  	  Quote: 	
		  

From: klinefelter.kevin(at)gmail.com <klinefelter.kevin(at)gmail.com>

Subject: Re: Rotax 912 ul engine problems

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

Date: Sunday, June 17, 2012, 10:09 AM



 --> RotaxEngines-List message posted by: klinefelter.kevin(at)gmail.com (klinefelter.kevin(at)gmail.com)



I believe it is very unlikely that the problem is ignition. Replace the spark plugs with the proper type and gap them properly. Do the pull test on all the plug caps. That should cover the most common ignition problems.

You mention a new throttle cable, and other carb parts. When we're the carbs last rebuilt? If its been several years I would start with having the carbs rebuilt properly. 

It is helpful to know what work was done to the engine immediately before the problem started. 

Kevin



On Jun 17, 2012, at 6:21 AM, Jóhann Jóhannsson <joeing701(at)simnet.is (joeing701(at)simnet.is)> wrote:



 	  Quote: 	
		   -->  RotaxEngines-List message posted by: =?ISO-8859-1?Q?J=F3hann_J=F3hannsson?= <joeing701(at)simnet.is (joeing701(at)simnet.is)>

 

 Hello list members.

 

 We really need your  expert help regarding a Rotax 912 ul 80 hp engine problem my friend has been dealing with for the past  three years or ever since he bought the plane.

 

 My friend bought this  Kitfox II aprox. 1990 model from USA and has been trying to solve a rough running engine problem, and is about to give up on the project.

 

 Here is the symptoms:

 

 Engine starts perfectly and runs on both mags with a drop within 100 rpm. When airborne the rough running starts around 3500-4500. Everything shakes very violently and aircraft looses altitude. Most often you can give it full power to continue flying, but when power is  reduced, the shaking starts again.

 

 What has been done:

 

 All fuel system has been checked, cleaned many times. Fuel pump replaced, including electrical pump added. Carbs have been cleaned, all jets replaced with new, new throttle cable. See here:

 http://www.chiefaircraft.com/aircraft/fuel-systems-carbs/throttle-cables-rotax/ma-mct100d048.html

 

 Everything has been adjusted and calibrated according to Rotax manual.  The mid range was suspected so we have tried to fine tune the jet needle by adjusting the clip, but does not seem to change anything.

 So we have almost ruled out fuel problems and are beginning to suspect the ignition system. Most likely the trigger system because the mag drop is within the normal drop, i.e. 90-100 rpm.

 The running of the  engine does not seem to change after it warms up, so the coils do not seem to be the problem.

 All wires have been checked and inspected.

 The engine sat for some time in a unheated trailer, before my friend bought the plane. He did clean the triggers of rust which had formed on the metal part.

 The triggers are really hard to reach on the Kitfox due to tight space between the firewall and engine.

 The engine will need to be removed to do any work on the charging and trigger system.

 Before we do that, I just wanted to ask you experts if you had any other ideas?

 

 Really appreciate any help.

 

 Best regards,

 Johann G.

 Iceland.

 

 

 

= Use the Matronics List Features --> http:========================http://www.matronics.com/contributio==============


	




	
 [quote][b]

Roger Lee

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

Posted: Sun Jun 17, 2012 9:35 am Post subject: Re: Rotax 912 ul engine problems

This really sounds like one carb trying to control one side of the engine at let's say 4400 rpm and the other at 4800 rpm. 

The other guys have good suggestions with the vent tubes being placed properly and new plugs gapped at .023 - .027. I hope the carbs have been totally rebuilt if not carbs that old need to be rebuilt for several reasons. The carbs need to be absolutely synced. It most likely isn't the ignition, but can't be ruled out just yet, but is improbable. The fuel systems back then didn't have re-circulation lines. You should have one especially if you have the new style fuel pump. Does it make any difference if he shuts down the electric pump? I wouldn't run it all the time, only when needed. An engine that old may have air leaks in a number of rubber part areas. I hope these have all been changed.

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

joeing701(at)simnet.is
Guest

Posted: Sun Jun 17, 2012 10:45 am Post subject: Rotax 912 ul engine problems

Thank you all for your advice.



The plugs are new and gapped at .025. Vent tubes are the same and have  

not been routed down in the airstream. Carbs have been synced with a  

new vacuum meter. The electric fuel pump has only been used after the  

new style pump was replaced. The electrical pump is only used to prime  

the system before start up and during take-off. Everything and I mean  

everything has been replaced in the carbs. New jets, rubber rings,  

bowl gasket and everything cleaned.  We even tried new carbs, but they  

were for a Rotax 914 and they just overfilled because of too much fuel  

pressure from the 912 fuel pump. We were told that the fuel pressure  

for 914 is lower.  When the engine started shaking, the fuel shut off  

valve in the carbs could not do its job with the higher pressure which  

caused the overfill situation.

The carb rubber socked has been replaced. All fuel lines are new. Do  

not know where you could have fuel leak in other rubber parts.

Roger, where would that be other than the carbs and the rubber socket?



Johann G.

Iceland.



On 17.6.2012, at 17:35, Roger Lee wrote:



 	  Quote: 	
		   

 >



 This really sounds like one carb trying to control one side of the  

 engine at let's say 4400 rpm and the other at 4800 rpm.

 The other guys have good suggestions with the vent tubes being  

 placed properly and new plugs gapped at .023 - .027. I hope the  

 carbs have been totally rebuilt if not carbs that old need to be  

 rebuilt for several reasons. The carbs need to be absolutely synced.  

 It most likely isn't the ignition, but can't be ruled out just yet,  

 but is improbable. The fuel systems back then didn't have re- 

 circulation lines. You should have one especially if you have the  

 new style fuel pump. Does it make any difference if he shuts down  

 the electric pump? I wouldn't run it all the time, only when needed.  

 An engine that old may have air leaks in a number of rubber part  

 areas. I hope these have all been changed.



 --------

 Roger Lee

 Tucson, Az.

 Light Sport Repairman - Maintenance Rated

 Rotax Repair Center - Heavy Maint. Rated

 Home 520-574-1080  TRY HOME FIRST

 Cell 520-349-7056





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=375916#375916

Roger Lee

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

Posted: Sun Jun 17, 2012 11:20 am Post subject: Re: Rotax 912 ul engine problems

Hi Johann,



The other places would have been the carb sockets, fuel hose and the "O" rings in the carb, but you have all these done. Are the needle clips in the #3 position? If you have a new style mechanical Rotax fuel pump you must have a re-circulation line. Over pressure could cause this problem. The 914 carbs should have worked except the #1-3 carb needle is in the #2 needle clip position. Have the engine mounts been replaced? This would cause a shake and affect the carbs. Have you done a differential compression test?



If I read your post right, the engine runs smooth up to 3500 and then it starts to shake up to 4500 and then as you go past that and up into higher rpms the shake quits?



If this is the case then I would want someone who really knows the Rotax carbs to take a look and check the needle and main jet sizes and alignment of all aligned parts. Something seems amiss here.

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

joeing701(at)simnet.is
Guest

Posted: Sun Jun 17, 2012 12:14 pm Post subject: Rotax 912 ul engine problems

The needle clips are in #3 position. The new pump has a over-pressure   

line out which should be routed to the same place as the carb overfill  

lines. The engine mounts have not been replaced since my friend bought  

the plane, and most likely not by the previous owner. We will look at  

that.

Last time we ran the engine, the rpm was a little higher when the  

shaking started, i.e. above 4500 rpm. It seem to vary a little in this  

higher range. Not alway in the mid range. If anyone is the expert in  

Rotax carbs in Iceland, it would be us. We have probably worked on the  

the most 

All the needle and jet sizes are according to the Rotax manual for the  

80 hp Rotax 912 ul engine.  All new.



Thank you again for all the advice. We will check the engine mounts.



Best regards,

Johann G.

Iceland.

On 17.6.2012, at 19:20, Roger Lee wrote:



 	  Quote: 	
		   

 >



 Hi Johann,



 The other places would have been the carb sockets, fuel hose and the  

 "O" rings in the carb, but you have all these done. Are the needle  

 clips in the #3 position? If you have a new style mechanical Rotax  

 fuel pump you must have a re-circulation line. Over pressure could  

 cause this problem. The 914 carbs should have worked except the #1-3  

 carb needle is in the #2 needle clip position. Have the engine  

 mounts been replaced? This would cause a shake and affect the carbs.  

 Have you done a differential compression test?



 If I read your post right, the engine runs smooth up to 3500 and  

 then it starts to shake up to 4500 and then as you go past that and  

 up into higher rpms the shake quits?



 If this is the case then I would want someone who really knows the  

 Rotax carbs to take a look and check the needle and main jet sizes  

 and alignment of all aligned parts. Something seems amiss here.



 --------

 Roger Lee

 Tucson, Az.

 Light Sport Repairman - Maintenance Rated

 Rotax Repair Center - Heavy Maint. Rated

 Home 520-574-1080  TRY HOME FIRST

 Cell 520-349-7056





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=375924#375924

ptag.dev(at)tiscali.co.uk
Guest

Posted: Sun Jun 17, 2012 12:14 pm Post subject: Rotax 912 ul engine problems

What colour are the plugs?

Regards

\Bob Harrison \G-PTAG



--

KeysFox

Joined: 05 Jan 2009
Posts: 137

Posted: Sun Jun 17, 2012 12:18 pm Post subject: Rotax 912 ul engine problems

A big thanks to Roger for sharing his training, experience and time.



Lockwood Aviation (Sebring, Florida) has had a Rotax technician available

by phone (863-655-6229) between 9 and 10 am and 2-3 pm east coast US time

daily.



If a solution does not materialize, they may be able to help. Be prepared

to hold as your call is taken in sequence with other callers.



BJ

Kitfox IV 912

 > 

 	  Quote: 	
		  

 This really sounds like one carb trying to control one side of the engine

 at let's say 4400 rpm and the other at 4800 rpm.

 The other guys have good suggestions with the vent tubes being placed

 properly and new plugs gapped at .023 - .027. I hope the carbs have been

 totally rebuilt if not carbs that old need to be rebuilt for several

 reasons. The carbs need to be absolutely synced. It most likely isn't the

 ignition, but can't be ruled out just yet, but is improbable. The fuel

 systems back then didn't have re-circulation lines. You should have one

 especially if you have the new style fuel pump. Does it make any

 difference if he shuts down the electric pump? I wouldn't run it all the

 time, only when needed. An engine that old may have air leaks in a number

 of rubber part areas. I hope these have all been changed.



 --------

 Roger Lee

 Tucson, Az.

 Light Sport Repairman - Maintenance Rated

 Rotax Repair Center - Heavy Maint. Rated

 Home 520-574-1080  TRY HOME FIRST

 Cell 520-349-7056





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=375916#375916

_________________
B Jones
N154K
443-480-1023

joeing701(at)simnet.is
Guest

Posted: Sun Jun 17, 2012 1:51 pm Post subject: Rotax 912 ul engine problems

Just confirmed from my friend that the compression was checked when he  

bought the plane and the total hours were 150 hours. Good and even  

compression. Engine mounts are as new. Spark plug color is light brown  

on all plugs.

We will borrow carbs from a friends plane this week and do a total  

swap. That would eliminate all fuel problems. I will keep you posted  

after that.



Thank you all for your advice and a special thanks to Roger.



Johann G.

Iceland.

On 17.6.2012, at 20:17, bjones(at)dmv.com wrote:



 	  Quote: 	
		   



 A big thanks to Roger for sharing his training, experience and time.



 Lockwood Aviation (Sebring, Florida) has had a Rotax technician  

 available

 by phone (863-655-6229) between 9 and 10 am and 2-3 pm east coast US  

 time

 daily.



 If a solution does not materialize, they may be able to help. Be  

 prepared

 to hold as your call is taken in sequence with other callers.



 BJ

 Kitfox IV 912

> 

> >

>

> This really sounds like one carb trying to control one side of the  

> engine

> at let's say 4400 rpm and the other at 4800 rpm.

> The other guys have good suggestions with the vent tubes being placed

> properly and new plugs gapped at .023 - .027. I hope the carbs have  

> been

> totally rebuilt if not carbs that old need to be rebuilt for several

> reasons. The carbs need to be absolutely synced. It most likely  

> isn't the

> ignition, but can't be ruled out just yet, but is improbable. The  

> fuel

> systems back then didn't have re-circulation lines. You should have  

> one

> especially if you have the new style fuel pump. Does it make any

> difference if he shuts down the electric pump? I wouldn't run it  

> all the

> time, only when needed. An engine that old may have air leaks in a  

> number

> of rubber part areas. I hope these have all been changed.

>

> --------

> Roger Lee

> Tucson, Az.

> Light Sport Repairman - Maintenance Rated

> Rotax Repair Center - Heavy Maint. Rated

> Home 520-574-1080  TRY HOME FIRST

> Cell 520-349-7056

>

>

> Read this topic online here:

>

> http://forums.matronics.com/viewtopic.php?p=375916#375916

>

Vic Peters

Joined: 30 Oct 2009
Posts: 54
Location: Millinocket, Maine

Posted: Sun Jun 17, 2012 4:19 pm Post subject: Rotax 912 ul engine problems

Sync and re sync the  carbs

   [quote][b]

_________________
Vic
912ul Xtra
Maine
Too old to cut the mustard but not the cheese.

joeing701(at)simnet.is
Guest

Posted: Sun Jun 17, 2012 4:43 pm Post subject: Rotax 912 ul engine problems

Thank you Vic.



That has been done after every adjustment of the cables and many more. Everything is in very good sync all through. We are still trying to find out if there is any binding in the carb throttle valve. We will change out the carbs this week and find out then.

Thanks 

Johann G.

Iceland.

On 18.6.2012, at 00:18, vic wrote:

 	  Quote: 	
		  Sync and re sync the carbs

 	  Quote: 	
		  



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

href="http://forums.matronics.com">http://forums.matronics.com

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



	


	


 [quote][b]

fgoggio(at)yahoo.com
Guest

Posted: Sun Jun 17, 2012 5:16 pm Post subject: Rotax 912 ul engine problems

Johan.i had. A problem like you are having on a older model 912 the carbs. Were rebuilt three times by rotax repairman. Carbs sycted.over and over.findly put new carbs on.still had problems.replaced. ignition modeals.still had.problems.all started lile yours.findly found the problem to be in the redrive system.needed to be re built.problems wemt away.mine started in flgjt at 4500 rpm.drove the rotax man crazy.swore it could not be the redrive

But was..spmething else to think about.good luck

Frank goggio. Wilmington. Nc



Sent from my Verizon Wireless 4G LTE DROID

-----Original message-----

[quote]From: "JÃ³hann JÃ³hannsson" <joeing701(at)simnet.is>

To: rotaxengines-list(at)matronics.com

Sent: Sun, Jun 17, 2012 20:42:47 EDT

Subject: Re: RotaxEngines-List: Rotax 912 ul engine problems

Thank you Vic.



That has been done after every adjustment of the cables and many more. Everything is in very good sync all through. We are still trying to find out if there is any binding in the carb throttle valve. We will change out the carbs this week and find out then.

Thanks 

Johann G.

Iceland.

On 18.6.2012, at 00:18, vic wrote:

[quote]Sync and re sync the carbs

 	  Quote: 	
		  


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

href="http://forums.matronics.com">http://forums.matronics.com

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


	


[b]

joeing701(at)simnet.is
Guest

Posted: Sun Jun 17, 2012 6:42 pm Post subject: Rotax 912 ul engine problems

Hello Frank.

Thank you very much for that information. This is something we will definitely look into. What kind of gear box did you have? The standard 2,27 or with the slipper clutch?

Best regards,

Johann G.

Iceland.



On 18.6.2012, at 01:16, fgoggio(at)yahoo.com (fgoggio(at)yahoo.com) wrote:

[quote]Johan.i had. A problem like you are having on a older model 912 the carbs. Were rebuilt three times by rotax repairman. Carbs sycted.over and over.findly put new carbs on.still had problems.replaced. ignition modeals.still had.problems.all started lile yours.findly found the problem to be in the redrive system.needed to be re built.problems wemt away.mine started in flgjt at 4500 rpm.drove the rotax man crazy.swore it could not be the redrive

But was..spmething else to think about.good luck

Frank goggio. Wilmington. Nc



Sent from my Verizon Wireless 4G LTE DROID

-----Original message-----

 	  Quote: 	
		  From: "Jóhann Jóhannsson" <joeing701(at)simnet.is (joeing701(at)simnet.is)>

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

Sent: Sun, Jun 17, 2012 20:42:47 EDT

Subject: Re: Rotax 912 ul engine problems

Thank you Vic.



That has been done after every adjustment of the cables and many more. Everything is in very good sync all through. We are still trying to find out if there is any binding in the carb throttle valve. We will change out the carbs this week and find out then.

Thanks 

Johann G.

Iceland.

On 18.6.2012, at 00:18, vic wrote:

 	  Quote: 	
		  Sync and re sync the carbs

 	  Quote: 	
		  



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

href="http://forums.matronics.com">http://forums.matronics.com

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



	






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

href="http://forums.matronics.com">http://forums.matronics.com

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



	






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

href="http://forums.matronics.com">http://forums.matronics.com

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

	
l>

[b]

fgoggio(at)yahoo.com
Guest

Posted: Mon Jun 18, 2012 2:05 am Post subject: Rotax 912 ul engine problems

We have tbe regular gear box.2,27.tbe way we found it we took the prop of and ran the engine.if you this be sure to do this at low rpm. Frank


Sent from my Verizon Wireless 4G LTE DROID


-----Original message-----

From: "JÃ³hann JÃ³hannsson" <joeing701(at)simnet.is>

To: rotaxengines-list(at)matronics.com

Sent: Sun, Jun 17, 2012 22:41:47 EDT

Subject: Re: RotaxEngines-List: Rotax 912 ul engine problems


Hello Frank.


Thank you very much for that information. This is something we will  

definitely look into. What kind of gear box did you have? The standard  

2,27 or with the slipper clutch?


Best regards,

Johann G.

Iceland.



On 18.6.2012, at 01:16, fgoggio(at)yahoo.com wrote:


 	  Quote: 	
		   Johan.i had. A problem like you are having on a older model 912 the  

 carbs. Were rebuilt three times by rotax repairman. Carbs  

 sycted.over and over.findly put new carbs on.still had  

 problems.replaced. ignition modeals.still had.problems.all started  

 lile yours.findly found the problem to be in the redrive  

 system.needed to be re built.problems wemt away.mine started in  

 flgjt at 4500 rpm.drove the rotax man crazy.swore it could not be  

 the redrive

 But was..spmething else to think about.good luck

 Frank goggio. Wilmington. Nc


 Sent from my Verizon Wireless 4G LTE DROID



 -----Original message-----

 From: "JÃ³hann JÃ³hannsson" <joeing701(at)simnet.is>

 To: rotaxengines-list(at)matronics.com

 Sent: Sun, Jun 17, 2012 20:42:47 EDT

 Subject: Re: RotaxEngines-List: Rotax 912 ul engine problems




 Thank you Vic.


 That has been done after every adjustment of the cables and many  

 more. Everything is in very good sync all through. We are still  

 trying to find out if there is any binding in the carb throttle  

 valve. We will change out the carbs this week and find out then.


 Thanks

 Johann G.

 Iceland.

 On 18.6.2012, at 00

Thom Riddle

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

Posted: Mon Jun 18, 2012 3:16 am Post subject: Re: Rotax 912 ul engine problems

One thing I have found to cause rough running is poor connection between the spark plug wires and spark plug connector/cap.  I've run across this several times. Make sure all are screwed in all the way clock-wise. After the first time I encountered this, I always check them on each condition inspection and mark the intersection with torque-seal or equivalent so they can be visually checked in the future.

_________________
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Dick Maddux

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

Posted: Mon Jun 18, 2012 3:46 am Post subject: Rotax 912 ul engine problems

Johann,

  As Frank mentioned ,we too had a similar problem in a Paradise P-1.  It would be rough in mid range.It was silky smooth so long as full power  was applied (as in climbout) but upon power reduction the roughness would  start and the airplane would vibrate like hell ! At one point during  troubleshooting, I even shut the engine down and glided the airplane thru  various speeds to see if it was airframe related ...it wasn't.

  It drove us nuts trying to find it. We changed props,tightened  mounts,checked/synced carbs,etc,etc. Finally we sent the gearbox off to Lockwood  for a re shim/rebuild as a last resort  and that did it ! The engine  did not have that much time and I would have sworn that was not the problem but  it fixed it !

  My Kitfox had a similar problem but I was able to fix it by replacing  the throttle cables as one of them was apparently slightly sticking at mid  range throwing the carbs out of balance. Check the "swivel" nuts on the carbs  for sticking also.

  That is my two cents.

                  Good luck !!

                               Dick Maddux

                               Milton,Fl

 [quote][b]

sdemeyer

Joined: 31 Jul 2009
Posts: 45

Posted: Mon Jun 18, 2012 5:16 am Post subject: Rotax 912 ul engine problems

Same exact problem here. Rebuilt carbs several times and changed many ignition components and nothing worked. After months of troubleshooting I gave up and flew the plane to a Rotax dealer. He rebuilt the gearbox and the problem went away. I had about 500 hours on the gearbox, 80HP Rotax.



[quote]

[b]

Roger Lee

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

Posted: Mon Jun 18, 2012 11:59 am Post subject: Re: Rotax 912 ul engine problems

Hi All,



Gearbox's can certainly cause engine roughness, but I personally find the owners with Vernier type throttle cables to have more issues than others. The thicker wire to these type cables causes them to slightly stick in the sheath and when you operate the throttle one carb won't go back to exactly the same place. This makes one side of the engine try to run at let's say 5000 rpm while the other side tries to run at 5300 rpm. This opposing action makes things rough and not good for the long term health of the engine. This can make the carb sync procedure an headache too.

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Tucson, Az.
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Light Sport Repairman
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craig(at)craigandjean.com
Guest

Posted: Mon Jun 18, 2012 12:46 pm Post subject: Rotax 912 ul engine problems

 	  Quote: 	
		   The thicker wire to these type cables causes them to slightly stick in the

sheath and when you operate the throttle one carb won't go back to exactly
	


the same place.



Are you referring to vernier throttles where the cables spit at the

throttle. McFarLane makes this one:

 

http://www.mcfarlane-aviation.com/Details.aspx?Article=199



I don't see how what you are describing could happen with a conventional

vernier throttle where there is only a single cable that connects to an

external splitter.



-- Craig

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