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912 UL runing on 3 cylinders

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iworonko(at)cox.net
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Posted: Sun Jul 06, 2008 3:35 pm Post subject: 912 UL runing on 3 cylinders

Hi folks,

 had a new problem show up about a week ago.   Before I start the engine I crank it with the mags off and choke on  for  2-3 seconds then turn the mags on and it fires right up.

 This time when I cranked it  I noticed it  didn't sound right, when I turned the mags on and started it, it ran very rough.  Before shutting it down did a mag check and both sides were working. Checked the  exhaust pipes and one was cold. pulled the cover off the cold cylinder to check  the valve train- everything looked good. Removed lower plugs on all cylinders  and did a compression test- all cylinders were same. So I put everything  together and tried running it again-ran just fine.

 This same scenario has repeated several consecutive  days. Its getting to a point where I can predict when its going to run on 3  cylinders by turning the prop by hand. There is a point where there should be a  compression stroke but its not there, prop spins free past it.  Everyday I  have been able to get it to run ok by either alternately cranking it with a  starter and by hand or doing a compression test. After a good start I go flying  and it performs flawlessly. Right after shut down it restarts fine, but  next day I can almost guaranty that it will do it all over  again.

 Any ideas?

 Eric  Speedster N58EW

  

  

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Fox5flyer
Guest

Posted: Sun Jul 06, 2008 5:21 pm Post subject: 912 UL runing on 3 cylinders

Sticking valve, rocker?

 Deke

  

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kitfoxmike

Joined: 05 Dec 2006
Posts: 373

Posted: Sun Jul 06, 2008 5:29 pm Post subject: Re: 912 UL runing on 3 cylinders

carbon buildup.  try marvel mystery oil in the fuel.  What you really need to do is decarbon the engine.  And yes, mine has done this.  Not in the last 2 years tho.

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JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Mon Jul 07, 2008 8:10 am Post subject: Re: 912 UL runing on 3 cylinders

My Rotax 912-S has also done something like this.  It is not to the point of running on 3 cylinders, but every couple months I spin the prop cold by hand and there is no compression on one cylinder...  I start it up, it flys perfect, and on the ground I have compression on all cylinders cold for the next several weeks when I spin the prop.  Its only every couple months that I spin the prop and find no compression on one cylinder.  I don't think its carbon though, as my engine did this with less than 25 hours on it, and its never seen a drop of 100LL



Mike

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