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Engine running rough at 3400 RPM and above

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dougsnash

Joined: 14 Apr 2008
Posts: 281

Posted: Fri Aug 06, 2010 8:40 am Post subject: Engine running rough at 3400 RPM and above

I think I have my rough running engine issues sorted out.  I spent several hours at Oshkosh harassing the tech gurrus from CPS, Lockwood, LEAF and Missippi.  They all had some interesting things to say but had no smoking gun for me.  Basically, soak the carbs for a couple of hours in a carb cleaner or a laquer thinner type solution and try them again.



The tech from lockwood suggested that perhaps I was actually running rich rather than lean.  He said that at higher RPMs the enrichener circuit actually leans out the mixture after its initial shot of fuel.  This got me thinking.



After re-assembling my carbs and re-installing them on the plane, I decided that I didn't like how close my enrichener cables were to my carb heat cable.  I adjusted the geometry so that there was more clearance.  This adjustment made it so that the enrichener would not close completely.  With a little further playing around the enricheners are now functioning correctly.  However, now that I've looked at it, I'm pretty sure that they were not closing correctly before either.  AHA, a smoking gun.



Last night I performed a complete re-balance for the carbs and ran the engine up.  I have a minor roughness at idle that was not there before but was able to run up to 5200 RPM static (on the tach) and the engine ran perfectly smoothly.



Today I am going to double check the idle mixtures and that should fix up the rough idle.



Thanks to all of you that gave me suggestions.  This has been a bit of a learning experience.  I knew it would be something simple but it was just a matter of finding the cause.



Doug MacDonald

CH-701 Scratch Builder

NW Ontario, Canada

912 UL

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Dick Maddux

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

Posted: Sat Aug 07, 2010 3:34 am Post subject: Engine running rough at 3400 RPM and above

Thanks for the info Doug.

  We still have a "vibration " at cruise rpm that I am trying to chase down on this Paradise we have been working on It went away after a gearbox reshim/respring but now is back. We are just finishing up a different prop installation to see if that helps with the issue (owner wanted to do this,not my idea)

  I have checked all the cables,swivlenuts ,etc in the carbs but will no another recheck. Sync is spot on.

  I now have the prop balancer so will check that out on the Warp we are removing. (as well as the internals)

                                                                         Dick Maddux

                                                                         Milton,Fl

  [quote][b]

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rparigoris

Joined: 24 Nov 2009
Posts: 797

Posted: Sat Aug 07, 2010 11:20 am Post subject: Engine running rough at 3400 RPM and above

Hi Dick"We still have a "vibration " at cruise rpm that I am trying to chase down"I remember hearing from a 912 guy who worked on Katanas that if you don't get the large washer on the crankshaft that holds gearbox on centered it can cause viabration.Probably worth considering to have dynamic balance, make absolute sure prop blades are tracking and are at same pitch before.Ron P.   [quote][b]

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malannx(at)bigpond.com
Guest

Posted: Sun Aug 08, 2010 4:19 am Post subject: Engine running rough at 3400 RPM and above

If anyone pulls gearbox off, a must do is to check the torque on the  crankshaft gear. Requires a deep 41mm  socket or 1and 5/8". Rotax mechanic  showed me a crankshaft that had the splines trashed by a loose gear. Will  produce vibrations you can't cure otherwise. Even gave me a new belville washer  in anticipation I would find mine loose - I did. He had seen enough of them  loose that a torque check was mandatory if the gearbox was off. If below torque  the nut must come off and a careful check of the striations on the bellville  washer will show if there had been any movement. If any shine on the striations  a new washer is a must(and loctite). When swinging on the end of the torque  wrench, I remember thinking about the "agony" the little crankshaft locking pin  was going through.

 Malcolm Ferguson

   [quote][b]

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Dick Maddux

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

Posted: Sun Aug 08, 2010 4:32 am Post subject: Engine running rough at 3400 RPM and above

Ron,

  Thanks for your reply. It seems we may have captured this problem. 

 Yesterday (in 106 degree heat) we removed the Warp propellor and installed the lighter Kiev and after much "tweaking " of the pitch were able to get a nice 'turbine smooth" engine. 

  I hope this will last and that the Owner of the Paradise P-1 will be happy. We (the AI and I) have sure worked hard to try and find out the reason forthe vibration.(pitch,tracking checked out fine on the Warp)

  The tech at Lockwoodstatet to me that they had  had a similar problem on another aircraft in the past. They almost tore an engine down trying to chase it but as a last effort replaced the prop and that was it!

  I intend on using my new balancer(thanks to Roger) to check out the Warp. The mystery is how it occurred. The plane was on a cross country from Montana to Pensacola, Fl and was running fine until over Mississippi and then the vibration started.

  We will probably pull the blades and look at the hub, blade ends. do a dye penetrent check for cracks,etc

  I am not totally convinced the prop is the problem but time will tell.

  The only other time I have run into this type of a problem was on an Aerotrec (former Euro Fox) based in the mountains of NC. The owner of the aircraft had a rough runner at cruise and we did everything to smooth it but nothing worked. The plane only had 40 hrs since new and everything was spot on ! (carb sync, cable movement,swivel nuts,ignition,etc) I told the owner that the only thing left was the prop but neither one of us could believe that was the problem. It was new out of the factory properly pitched,etc.

 I had to return from my vacation in NC and could no longer help him. He called the factory and they came down, replaced the prop and problem solved. Seems this was one of 3 that were defective. So, it does happen.

                                                 Dick Maddux

                                                  912UL

                                                   Milton,Fl

  [quote][b]

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rparigoris

Joined: 24 Nov 2009
Posts: 797

Posted: Sun Aug 08, 2010 9:19 pm Post subject: Engine running rough at 3400 RPM and above

Hi DickHere is a nice rundown of some causes of viabration:http://www.rotaxservice.com/rotax_tips/rotax_vibration.htmRon Parigoris   [quote][b]

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Dick Maddux

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

Posted: Mon Aug 09, 2010 4:25 am Post subject: Engine running rough at 3400 RPM and above

Thanks for the info Ron !

 Roger, Thanks for the "show and tell" That was great ! 

                                     Dick Maddux

                                     Milton,Fl

  [quote][b]

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