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peteohms
Joined: 31 Oct 2007
Posts: 224
Location: Leander, TX
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 Posted: Sat May 09, 2009 2:32 pm Post subject: 912 One cylinder running rich |
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I just replaced the plugs on my 912 and the two plugs on the left front cylinder were black. The rest were normal. (+/-436 hours on the engine) I tried to remove the valve cover but the wrench just bent. Two questions:
1) What would cause the one cylinder to run rich?
2) How should I go about getting the bolt loose on the valve cover without stripping the allen head or breaking the allen wrench?
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Pete
Leander, TX
Kitfox III, 912ul, Grove |
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williamtsullivan(at)att.n
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| Posted: Sat May 09, 2009 3:02 pm Post subject: 912 one cylinder running rich |
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To get the Allen screw out, take a soft punch- aluminum or brass- and give it a couple of taps with a small hammer. That should shake it loose. Or, go to your local auto parts store to the K-D tool rack and get an impact driver. Cheap and effective, but you need a set of 3/8" drive metric Allen wrenches. Good luck.
Bill Sullivan
Windsor Locks, Ct.
Kolb Firestar, 447
[quote][b]
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Sat May 09, 2009 7:00 pm Post subject: Re: 912 One cylinder running rich |
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Hi Pete,
Bill is right about a few taps. Have someone put a little pressure on the screw and while he is trying to turn it just tap it with something like a brass or aluminum rod a time or two right on the edge of the screw. It will come loose.
The different lengths in the intake manifolds combined with idle rpms can cause the black sooty plugs at times. It is very common and goes away when you are at higher rpms like cruise. I wouldn't lose any sleep over it.
I wouldn't take the valve cover off unless there is a real need. It is an "O" ring seal and sometimes won't seal tight again and will ooze oil. Then you need to replace the "O" ring. A set of 4 valve cover "O" rings may not be quite as cheap as you might think. $28 each plus $5 for the small "O" ring for the screw itself.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
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Ivor Phillips
Joined: 16 Jan 2006
Posts: 253
Location: London UK
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| Posted: Sun May 10, 2009 1:58 am Post subject: 912 One cylinder running rich |
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Before you thump the allen bolt with a impact tool, Use some localised heat to its head, Give it time to heat soak the loctite, then it should remove easily,
Dont forget to reapply loctite for fitting,
regards
Ivor
---- peteohms <apeterchristensen(at)sbcglobal.net> wrote:
| Quote: |
I just replaced the plugs on my 912 and the two plugs on the left front cylinder were black. The rest were normal. (+/-436 hours on the engine) I tried to remove the valve cover but the wrench just bent. Two questions:
1) What would cause the one cylinder to run rich?
2) How should I go about getting the bolt loose on the valve cover without stripping the allen head or breaking the allen wrench?
--------
Pete
Hell Paso, TX
Kitfox III, 912ul, Grove
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p 43313#243313
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peteohms
Joined: 31 Oct 2007
Posts: 224
Location: Leander, TX
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| Posted: Sun May 10, 2009 12:16 pm Post subject: 912 One cylinder running rich |
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Thank you Bill and Roger. The 2 plugs were the only 2 with carbon. All the
others were fine. I thought maybe a valve was sticking or something. The A
and P who did my owner assisted annual thought so too. He has a rotax in
his Kitfox but is a relatively new owner like me. I had to fly about 90
miles to get my annual done so I thought the plugs should all be the same.
Mag check shows no difference, if that makes any difference.
Pete
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Pete
Leander, TX
Kitfox III, 912ul, Grove |
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Float Flyr
Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland
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| Posted: Sun May 10, 2009 3:49 pm Post subject: 912 One cylinder running rich |
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If you are really worried about it try a differential compression test.
Noel
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Noel Loveys
Kitfox III-A
Aerocet 1100 Floats |
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Sun May 10, 2009 6:38 pm Post subject: Re: 912 One cylinder running rich |
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I work on lots of Rotax 912's and most have it at some time. Sometimes they don't and sometimes they do. It just depends on the circumstances within the last few to several minutes before you shut it down, but I see it all the time. It's nothing to worry about because it is not like that at higher rpms or even at idle all the time.
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Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
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K Dilks
Joined: 22 Sep 2008
Posts: 108
Location: UK
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| Posted: Sun May 10, 2009 11:58 pm Post subject: Re: 912 One cylinder running rich |
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If No1 cyl really runs rich at idle it can be the idle jet is getting blocked. I know this sounds wrong but bear with me.
As Roger says the inlet manifold distributes the fuel not so well at low speeds but if the idle jet gets blocked cyl 1 runs rich from fuel being pulled by the high vacuum through the main jet, but this does not atomize well and goes to number 1 at idle.
When fully block it will flood No1 and run on 3 cylinders.
When the engine speeds up to about 2200 rpm the situation is reversed and cyl 3 get the rich mix.
Blow out the small idle jet and check idle mixture screw is no more that 1 1/2 turns open.
Hope this is clear
Kev
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Mon May 11, 2009 3:33 am Post subject: Re: 912 One cylinder running rich |
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Pete,
In addition to what others have said about unequal air/fuel distribution at low engine speed, there is one other possibility. This occurred on a 912UL in an Allegro 2000. It turned out to be a partially broken light gage wire in the ignition circuit. I can't tell you which wire it was but the insulation was white in color and it was very light gage, probably #18 or #20.
Before we found the partially broken wire and repaired it, the plugs in #1 cylinder were always very sooty. There was no differential compression problem and no perceptible loss of power. After the repair, the front cylinder plugs were still darker than the rear cylinder plugs but not like before the repair.
So if all else fails to cure the sooty front plugs, do an thorough examination of every inch of your ignition system wiring. You may find a partial break as I did.
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Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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