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dougsnash

Joined: 14 Apr 2008
Posts: 281

Posted: Sun Jul 04, 2010 5:25 pm Post subject: rough running at 3400 RPM and above

Finally, after just over four years of building I am to the point of test running the engine on my CH-701.  Not surprising me at all, I am having an issue or two along the way. 



The engine runs great from idle of about 1850RPM up to around 3400 RPM and then starts running rough and bogging out.  If I pull the carb heat on or pull on the enrichener I can get it up to about 4000RPM before the roughness starts.  This would suggest to me I am running lean.



My engine is a 1999 vintage 912UL with the older style Rotax log carb heat plenum.  This was a used engine that I got from a scrapped CH-701.  There are about 13 hours on the engine before the plane was damaged and not repaired.  The engine was run on a test stand three and a half years ago but has not run since.



So far I have pulled the float bowls off and cleaned out the main and idle jets, removed the gunk from the float bowls, and cleaned the little orifice in the corner of the float bowl.  After doing this the engine starts and idles great.



I have done a mechanical syncronization and think I have a fairly good pnumatic one too.  At least the needles on the lockwood syncro gauges move at the same time.  Not quite the same amount though.  If it makes any difference I am running 100LL for test purposes so octane shouldn't be an issue.



Any suggestions as to why I am getting bogging out at 3400 RPM?



Doug MacDonald

NW Ontario, Canada

rickofudall

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

Posted: Sun Jul 04, 2010 7:48 pm Post subject: rough running at 3400 RPM and above

Doug, Look for gunk around the needle jet, the needle itself and in the main jet. Also make sure the vent tube to the float chamber is clear.  Check the carb connector boots to make sure there are no cracks (you can miss this if you don't take them off and get them up to a strong light). Have you checked the plugs after a run up to where it starts to run rough at 3400 RPM? What EGT and CHT readings are you getting at the stumble point?

If you don't feel comfortable doing a full carb rebuild, you might want to consider having a shop do it. 

 



Rick Girard



On Sun, Jul 4, 2010 at 8:18 PM, MacDonald Doug <dougsnash(at)yahoo.com (dougsnash(at)yahoo.com)> wrote:

[quote] --> RotaxEngines-List message posted by: MacDonald Doug <dougsnash(at)yahoo.com (dougsnash(at)yahoo.com)>

 

 Finally, after just over four years of building I am to the point of test running the engine on my CH-701.  Not surprising me at all, I am having an issue or two along the way.

 

 The engine runs great from idle of about 1850RPM up to around 3400 RPM and then starts running rough and bogging out.  If I pull the carb heat on or pull on the enrichener I can get it up to about 4000RPM before the roughness starts.  This would suggest to me I am running lean.

  

 My engine is a 1999 vintage 912UL with the older style Rotax log carb heat plenum.  This was a used engine that I got from a scrapped CH-701.  There are about 13 hours on the engine before the plane was damaged and not repaired.  The engine was run on a test stand three and a half years ago but has not run since.

  

 So far I have pulled the float bowls off and cleaned out the main and idle jets, removed the gunk from the float bowls, and cleaned the little orifice in the corner of the float bowl.  After doing this the engine starts and idles great.

  

 I have done a mechanical syncronization and think I have a fairly good pnumatic one too.  At least the needles on the lockwood syncro gauges move at the same time.  Not quite the same amount though.  If it makes any difference I am running 100LL for test purposes so octane shouldn't be an issue.

  

 Any suggestions as to why I am getting bogging out at 3400 RPM?

 

 Doug MacDonald

 NW Ontario, Canada

 

 

 

 

 

 

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dougsnash

Joined: 14 Apr 2008
Posts: 281

Posted: Mon Jul 05, 2010 2:31 am Post subject: rough running at 3400 RPM and above

Thanks for your reply Richard.  A blocked vent tube might be the problem.  It seems like a venting issue to me.  I don't think the sockets are the source as they are new and are the new style with the spacer on the clamp.



I have not checked the plugs after stumbling yet, I'll try that on the next runnup.  They are also new and were gapped as per the manual at installation.



Doug MacDonald

 	  Quote: 	
		   From: Richard Girard <aslsa.rng(at)gmail.com>

 

 Doug, Look for gunk around the needle jet, the needle

 itself and in the main

 jet. Also make sure the vent tube to the float chamber is

 clear.  Check the

 carb connector boots to make sure there are no cracks (you

 can miss this if

 you don't take them off and get them up to a strong

 light).

 Have you checked the plugs after a run up to where it

 starts to run rough at

 3400 RPM? What EGT and CHT readings are you getting at the

 stumble point?

 If you don't feel comfortable doing a full carb rebuild,

 you might want to

 consider having a shop do it.

 

 Rick Girard

rampil

Joined: 04 May 2007
Posts: 870

Posted: Tue Jul 06, 2010 9:58 am Post subject: Re: rough running at 3400 RPM and above

Check to make sure there is not soot on the float bowls, a loose exhaust joint could boil the gas on one side when the engine power is set high enough

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dougsnash

Joined: 14 Apr 2008
Posts: 281

Posted: Tue Jul 06, 2010 5:57 pm Post subject: rough running at 3400 RPM and above

The saga continues...



Tonight I pulled the carbs right off of the plane.  I pulled them apart and this time got the float needles right out.  There was a small chunk of silicone beside the needle in one of the carbs but after removing it and running the engine, there was little improvment if any.  I was able to get it up to 4200 with the enrichener on but only the same old 3400 with the enrichener off.



Other things I have tried is raising the needle one notch to full rich.  This also made little to no difference. I stopped the engine while it was misfiring at 3400 RPM and pulled a couple of plugs.  They were sooty white so I think we can say that this issue is definately a lean misfire.



I read someplace in the parts manual that there are slightly larger main jets available when you run an air box.  Since I have the original cone filters, I removed the airbox and ran it with them (also on the richest needle setting) and again the engine stumbles at about 3400 RPM.



One thought I had tonight after all of this playing around is; is it possible that the throttle shaft o-rings could leak enough to cause this issue?  I don't know that they are leaking but given that the carbs are over ten years old, it is possible.



While I had the carbs apart I re-checked all of the other passages and found no buildup in any of them.  Getting frustrating but this wouldn't be any fun if it was easy.



Doug MacDonald

CH-701 Scratch Builder

912 UL

NW Ontario, Canada

rickofudall

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

Posted: Tue Jul 06, 2010 7:03 pm Post subject: rough running at 3400 RPM and above

Have you checked all the pieces of the equalizer line between the two intake manifolds? Try checking the vacuum readings at the equalizer and then at the carb taps with the equalizer line connected to see if there's any gross difference.  As long as you had the carbs off, did you pull the carb sockets and check them? I know you said they are recently replaced, but they're easy to check and it eliminates one more possible source of a leak. There was a bad batch a few years back that rotted out within a year. I couldn't see the cracks in mine until I got them off and used a strong light, then the cracks were obvious.

 What about the o-rings at the socket and those on the intake manifolds? 

Have you checked the diaphragms in the carb domes? You've had them out to raise the needle did you make sure the tab on the diaphragm is set in the slot in the carburetor body?

 Also, from the IPC, there are no o-ring seals on the throttle shafts? Have you miked them to see if the carb body is corroded or rotted out the throttle shaft bore?

Personally, I wouldn't start messing with jetting until you've exhausted every possibility of a gross air leak.

 



Rick Girard

On Tue, Jul 6, 2010 at 8:57 PM, MacDonald Doug <dougsnash(at)yahoo.com (dougsnash(at)yahoo.com)> wrote:

 [quote]--> RotaxEngines-List message posted by: MacDonald Doug <dougsnash(at)yahoo.com (dougsnash(at)yahoo.com)>

  

 The saga continues...

 

 Tonight I pulled the carbs right off of the plane.  I pulled them apart and this time got the float needles right out.  There was a small chunk of silicone beside the needle in one of the carbs but after removing it and running the engine, there was little improvment if any.  I was able to get it up to 4200 with the enrichener on but only the same old 3400 with the enrichener off.

  

 Other things I have tried is raising the needle one notch to full rich.  This also made little to no difference. I stopped the engine while it was misfiring at 3400 RPM and pulled a couple of plugs.  They were sooty white so I think we can say that this issue is definately a lean misfire.

  

 I read someplace in the parts manual that there are slightly larger main jets available when you run an air box.  Since I have the original cone filters, I removed the airbox and ran it with them (also on the richest needle setting) and again the engine stumbles at about 3400 RPM.

  

 One thought I had tonight after all of this playing around is; is it possible that the throttle shaft o-rings could leak enough to cause this issue?  I don't know that they are leaking but given that the carbs are over ten years old, it is possible.

  

 While I had the carbs apart I re-checked all of the other passages and found no buildup in any of them.  Getting frustrating but this wouldn't be any fun if it was easy.

 

 Doug MacDonald

 CH-701 Scratch Builder

 912 UL

 NW Ontario, Canada

 

 

 

 

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aoldman(at)xtra.co.nz
Guest

Posted: Wed Jul 07, 2010 12:56 am Post subject: rough running at 3400 RPM and above

When you stopped the engine to check the plugs did  you also check the fuel in the carb bowls. The fuel pump { or filter }may not be  delivering sufficent fuel to keep it running at high RPM settings. Have you  check the exhaust has not become obstructed while the engine was not being used  , that problem can also become apparent at high RPM . Just some more things  to check.

  

 Downunder

 MK111c

  

 [quote]   ---

joeing701(at)simnet.is
Guest

Posted: Wed Jul 07, 2010 2:57 am Post subject: rough running at 3400 RPM and above

Hello Doug.



My friend has a similar problem with his Kitfox and a few days ago he  

noticed that the primer line was broken and was sucking air. It was  

not the only cause for his rough running engine problem, but I think a  

few small air leaks can have a bad effect at hight rpm.

He had checked the primer pump and the lines but could not find any  

problems, until he took the line off the carb, he saw the broken line  

by the clamp on the carb.

I hope this helps in finding the cause of your rough  running engine.



Johann G.

CH-701

912 UL

Iceland.

On 7.7.2010, at 01:57, MacDonald Doug wrote:



 	  Quote: 	
		   

 >



 The saga continues...



 Tonight I pulled the carbs right off of the plane.  I pulled them  

 apart and this time got the float needles right out.  There was a  

 small chunk of silicone beside the needle in one of the carbs but  

 after removing it and running the engine, there was little  

 improvment if any.  I was able to get it up to 4200 with the  

 enrichener on but only the same old 3400 with the enrichener off.



 Other things I have tried is raising the needle one notch to full  

 rich.  This also made little to no difference. I stopped the engine  

 while it was misfiring at 3400 RPM and pulled a couple of plugs.   

 They were sooty white so I think we can say that this issue is  

 definately a lean misfire.



 I read someplace in the parts manual that there are slightly larger  

 main jets available when you run an air box.  Since I have the  

 original cone filters, I removed the airbox and ran it with them  

 (also on the richest needle setting) and again the engine stumbles  

 at about 3400 RPM.



 One thought I had tonight after all of this playing around is; is it  

 possible that the throttle shaft o-rings could leak enough to cause  

 this issue?  I don't know that they are leaking but given that the  

 carbs are over ten years old, it is possible.



 While I had the carbs apart I re-checked all of the other passages  

 and found no buildup in any of them.  Getting frustrating but this  

 wouldn't be any fun if it was easy.



 Doug MacDonald

 CH-701 Scratch Builder

 912 UL

 NW Ontario, Canada

Thom Riddle

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

Posted: Wed Jul 07, 2010 3:59 am Post subject: Re: rough running at 3400 RPM and above

Doug,



I suggest you go to http://www.bingcarburetor.com/manual.html



and buy their manual for US$11. With this you should be able to do a complete inspection and cleaning. A ten year old carburetor is likely to need new seals/o-rings. This is also an opportunity to make sure that the correct jets are in place. I've done many Bing 64 and Bing 94 carb cleaning and inspections and it is not uncommon to find carbs with the wrong jets installed and bad seals, especially on older ones.



If you don't feel comfortable doing the complete inspection and cleaning let me know. I do them for $50/carb plus parts and only replace parts that actually need replacing. I'm not trying to sell you a service because I feel that anyone who can build an airplane can do this work themselves with the proper documentation. But some are not comfortable going deep into their carburetors so I offer this service.



Thom Riddle

Buffalo, NY

http://sites.google.com/site/riddletr/a&pmechanix

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Buffalo, NY (9G0)

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

ami(at)mcfadyean.freeserv
Guest

Posted: Wed Jul 07, 2010 11:56 pm Post subject: rough running at 3400 RPM and above

There is also a filter in the mechanical fuel  pump.

 Obviously there is no way of cleaning  this.

 Only a fuel pressure test (measured downstream of  the pump) will give a clue as to whether its blocked.

  

 Duncan McF.

 [quote]   ---

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

Posted: Thu Jul 08, 2010 3:13 am Post subject: rough running at 3400 RPM and above

Hi! I’ve not been following this thread but the electrical fuel pumps also have a very fine thimble filter in the intake end  which needs VERY careful attention to remove it for inspection/cleaning and it is impossible to get a replacement filter .Returning this filter into its working location needs a very blunt instrument to push the filter into place from the bottom of the thimble shape taking care not to damage the gauze.  

Regards  

Bob Harrison.  

         

  

From: owner-rotaxengines-list-server(at)matronics.com [mailto:owner-rotaxengines-list-server(at)matronics.com] On Behalf Of Duncan & Ami McFadyean

 Sent: 08 July 2010 08:55

 To: rotaxengines-list(at)matronics.com

 Subject: Re: RotaxEngines-List: Re: rough running at 3400 RPM and above  

  

     

There is also a filter in the mechanical fuel pump.  

    

Obviously there is no way of cleaning this.  

    

Only a fuel pressure test (measured downstream of the pump) will give a clue as to whether its blocked.  

    

   

    

Duncan McF.  

  [quote]    

---

dougsnash

Joined: 14 Apr 2008
Posts: 281

Posted: Thu Jul 08, 2010 7:51 am Post subject: rough running at 3400 RPM and above

Thank you for all of the suggestions.  I'll be looking into these issues a little further this weekend.



Yesterday I ordered a complete overhaul kit for both carbs.  It's a little pricey but then everything will be new.  This morning I ordered the Bing manual.  I've probably spent more on the three gallons of 100LL I've burned troulbeshooting this issue than the cost of the manual.



Anyway, all of this stuff should be here Monday or Tuesday so hopefully I'll be running correctly by mid next week.  I'll keep you informed.



Thanks again



Doug MacDonald

CH-701

NW Ontario, Canada

dougsnash

Joined: 14 Apr 2008
Posts: 281

Posted: Wed Jul 14, 2010 6:14 pm Post subject: rough running at 3400 RPM and above

An update on my progress.  I recieved the carb rebuild kits and have installed them.  Tonight I ran the engine up and it runs a bit better but still not right.  Now I am able to get it up to 3800 before it starts to miss and bog down.  Again, I am still able to get it up to over 4000 RPM by pulling on the enrichener.



I performed a full carb sync on it today.  I was able to get the gauge needles to line up very nicely.  While I had the carbs off for cleaning and rebuild, I pulled the carb sockets off and they are like new, no indications of leaks.



I disconnected the fuel line where it goes into the engine fuel pump and checked for flow from the electric Facet I am using in lieu of gravity feed.  There is a steady stream of fuel coming form the the line.  I pulled the fuel lines at the carb and ran the Facet again and am getting lots out of the carb fittings too.



Next, I disconnected the airbox from the carb and had my assistant run the engine up.  I watched the carb slide and at 3800RPM, the slide was about two thirds to three quarters open.  About where I think it should be at that power level.



I'm starting to think this might be an ignition problem.  All of the plugs are new and I gapped them when I installed them but I don't recall now what I gapped them to.  I see in the maintenance manual it says to gap them to 0.027 to 0.031.  I'll have to check that tomorrow and see where they are at.



I don't know guys, any suggestions?



Doug MacDonald

CH-701, North Western Ontario, Canada

E. D. Eliot

Joined: 10 Feb 2007
Posts: 4
Location: Southern California - USA

Posted: Wed Jul 14, 2010 7:56 pm Post subject: rough running at 3400 RPM and above

No experience with Rotax yet but did solve a few 'automobile engine problems' by first checking the resistance of the high tension wires.  Once, I replaced spark plugs and one of the 'new' ones was bad.  God luck  - we;ll all learn from watching your progress.

 	  Quote: 	
		   Date: Wed, 14 Jul 2010 19:12:19 -0700

 From: dougsnash(at)yahoo.com

 Subject: Re: rough running at 3400 RPM and above

 To: rotaxengines-list(at)matronics.com

 --> RotaxEngines-List message posted by: MacDonald Doug <dougsnash(at)yahoo.com>

 An update on my progress.  I recieved the carb rebuild kits and have installed them.  Tonight I ran the engine up and it runs a bit better but still not right.  Now I am able to get it up to 3800 before it starts to miss and bog down.  Again, I am still able to get it up to over 4000 RPM by pulling on the enrichener.

 I performed a full carb sync on it today.  I was able to get the gauge needles to line up very nicely.  While I had the carbs off for cleaning and rebuild, I pulled the carb sockets off and they are like new, no indications of leaks.

 I disconnected the fuel line where it goes into the engine fuel pump and checked for flow from the electric Facet I am using in lieu of gravity feed.  There is a steady stream of fuel coming form the the line.  I pulled the fuel lines at the carb and ran the Facet again and am getting lots out of the carb fittings too.

 Next, I disconnected the airbox from the carb and had my assistant run the engine up.  I watched the carb slide and at 3800RPM, the slide was about two thirds to three quarters open.  About where I think it should be at that power level.

 I'm starting to think this might be an ignition problem.  All of the plugs are new and I gapped them when I installed them but I don't recall now what I gapped them to.  I see in the maintenance manual it says to gap them to 0.027 to 0.031.  I'll have to check that tomorrow and see where they are at.

 I don't know guys, any suggestions?

 Doug MacDonald

 CH-701, North Western Ontario, Canada

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Dick Maddux

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

Posted: Thu Jul 15, 2010 4:58 am Post subject: rough running at 3400 RPM and above

Doug ,

  Have you done a mag check? I had a rough runner and it showed up in the mag check. After much work,frustration,etc I called Ronnie Smith at South Mississippi Light Aircraft and he suggested I check the red power lead to the coils for a break. I used a sewing pin with an ohm meter and attached one lead  to the pin (the other to ground). By penetrating the plastic shielding of the wire I worked my way back along the wire and sure enough I found the break along a flat run. It was totally invisible from looking at it. With a cut and splice, I was back in business.

  You could call Ronnie. He is very helpful and sure knows these engines!

                                              Dick Maddux

                                              912 Ul

                                              Milton,Fl

sdemeyer

Joined: 31 Jul 2009
Posts: 45

Posted: Thu Jul 15, 2010 5:21 am Post subject: rough running at 3400 RPM and above

I know this will sound silly but, do verify your spark plugs wires are going to the correct cylinders. When I purchased my KF, I had a similar problem and found that the guy I purchased from had swapped a couple of ignition wires. Once I put them on the correct cylinders, problem went away. Download the Rotax heavy maintenance manual and compare with the schematics. 



Scott



--- On Thu, 7/15/10, Catz631(at)aol.com <Catz631(at)aol.com> wrote:

 	  Quote: 	
		  

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

Subject: Re: RotaxEngines-List: Re: rough running at 3400 RPM and above

To: rotaxengines-list(at)matronics.com

Date: Thursday, July 15, 2010, 5:56 AM



   Doug ,

  Have you done a mag check? I had a rough runner and it showed up in the mag check. After much work,frustration,etc I called Ronnie Smith at South Mississippi Light Aircraft and he suggested I check the red power lead to the coils for a break. I used a sewing pin with an ohm meter and attached one lead  to the pin (the other to ground). By penetrating the plastic shielding of the wire I worked my way back along the wire and sure enough I found the break along a flat run. It was totally invisible from looking at it. With a cut and splice, I was back in business.

  You could call Ronnie. He is very helpful and sure knows these engines!

                                              Dick Maddux

                                              912 Ul

                                              Milton,Fl 

    	  Quote: 	
		  http://www.matronics.com/Navigator?Rtarget="_blank"

el="nofollow" target="_blank" href="http://www.matronics.com/contribu=== 	


	
 [quote][b]

rayw

Joined: 18 Jul 2009
Posts: 25
Location: Wisconsin, Central

Posted: Thu Jul 15, 2010 6:26 am Post subject: Re: rough running at 3400 RPM and above

Doug,



I have had this problem you describe. Spraying carb cleaner into the jets and visually inspecting is not enough. You need to take a small piece of stiff wire and work it around the jet ofice to get the "crust" to break loose. This happened to me and the "crust" was in the main jet of just one carb.



I actually used the needle from the jet and not a piece of wire. I was careful not to bend the needle.



Ray

Gtblu

Joined: 18 Jul 2006
Posts: 37
Location: Australia

Posted: Thu Jul 15, 2010 2:34 pm Post subject: rough running at 3400 RPM and above

Hi  Doug,

  

 Have you tried a  diferent Prop. I had the oppertunity to try some diferent props a few years ago,  and each caused a diferent rough spot in the engine. Worth a go to eliminate  that as the problem.

  

 Cheers

  

 Gtblu

   [quote][b]

joeing701(at)simnet.is
Guest

Posted: Fri Jul 16, 2010 6:05 am Post subject: rough running at 3400 RPM and above

Hello Rotax owners.



My friend is also experiancing rough running on his Rotax 912 ul and has done all kinds of adjustments,replacing carb parts and cleaning, but is tearing the engine off to look at the electrical system. His plane is a Kitfox and the engine is to close to the firewall to do any inspection on the megnetos and ignition system.

We were wondering if anyone has replaced the spark plug wires without replacing the ignition coils? Are the wires screwed into the coils or glued?



Thanks,

Johann G.

Rotax 912 ul.

Zenith 701



Doug , 

Â Have you done a mag check? I had a rough runner and it showed up in the mag check. After much work,frustration,etc I called Ronnie Smith at South Mississippi Light Aircraft and he suggested I check the red power lead to the coils for a break. I used a sewing pin with an ohm meter andÂ attached one lead Â to the pin (the other to ground). By penetrating the plastic shielding of the wire I worked my way back along the wire and sure enough I found the break along a flat run. It was totally invisible from looking at it. With a cut and splice, I was back in business. 

Â You could call Ronnie. He is very helpful and sure knows these engines! 

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 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 Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â 912 Ul

Roger Lee

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

Posted: Sat Jul 17, 2010 2:03 pm Post subject: Re: rough running at 3400 RPM and above

The spark plug wires screw into each coil. The wires can be replaced. 

It may just be the air gap between the pick up coils and the sensor that needs adjusting. Bad grounds can cause these type of problems. If someone has just rebuilt the carbs just prior to this that is where I would look. Someone may have put a part in the wrong way. Yes there are a few parts that can be installed wrong.

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Tucson, Az.
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Light Sport Repairman
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