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JohnF
Joined: 13 May 2010
Posts: 124
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 Posted: Fri Jun 08, 2012 10:42 am Post subject: Rotallxl 912 ULS Mystery |
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After a nice runup last evening; that is, nice mag drops (about 100 on each side) and static rpm around 5050, and engine running smoothing.
This morning I took the plane out to fly...taxi to end of runway (about one mile) and did runup with oil temp 125-degrees F. Mag drop 330/360 - very untypical, and running rough. Static impossible to reach. Engine rpm decreased as throttle advanced past 4050 rpm or so....very rough...idle way too low...around 800 rpm.
Experienced RV builder and local A&P got involved. We tried all sorts of things; like removing the air filters...no difference....sometimes, not always, if top cowling was removed engine ran fine...sometimes not. Nothing touches the cowl when it is on so nothing is interfering with the engine due to cowl on or off. Only air flow may be different.
Reseated carbs after looking at the rubber ring they mount on...look OK..carbs secure. All controls smooth and move stop to stop.
Because engine SOMETIME ran well with top cowling off, we put it on and taped the oil filler door open to see if increased air flow would make any difference...it did not.
This is the third time the plane was just fine when put away and no good the following morning.
Temperatures have been moderate....high 40's at night, low 80's mid day.
Scat cooling from cowl to engine shroud secure and clear.
Pulling electric fuel pump fuse with engine running lowered fuel pressure slightly but made no difference in poor operation....nor does it make a difference with the engine is running well.
I am told that the definition of stupidity is doing the same thing over and over and expecting different results. I seem to be at that point now.
'Its still one giant mystery of intermittent good/bad operation.
John
[quote][b]
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williamtsullivan(at)att.n
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| Posted: Fri Jun 08, 2012 10:55 am Post subject: Rotallxl 912 ULS Mystery |
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Do you have rubber fuel lines (automotive type)? Feel them looking for soft spots or irregularities. Might be a flap in a line.
--- On Fri, 6/8/12, JohnF <n29cx(at)ridgeviewtel.us> wrote:
| Quote: |
From: JohnF <n29cx(at)ridgeviewtel.us>
Subject: RotaxEngines-List: Rotallxl 912 ULS Mystery
To: "rotax engines matronics" <rotaxengines-list(at)matronics.com>
Date: Friday, June 8, 2012, 2:42 PM
After a nice runup last evening; that is, nice mag drops (about 100 on each side) and static rpm around 5050, and engine running smoothing.
This morning I took the plane out to fly...taxi to end of runway (about one mile) and did runup with oil temp 125-degrees F. Mag drop 330/360 - very untypical, and running rough. Static impossible to reach. Engine rpm decreased as throttle advanced past 4050 rpm or so....very rough..idle way too low...around 800 rpm.
Experienced RV builder and local A&P got involved. We tried all sorts of things; like removing the air filters...no difference....sometimes, not always, if top cowling was removed engine ran fine...sometimes not. Nothing touches the cowl when it is on so nothing is interfering with the engine due to cowl on or off. Only air flow may be different.
Reseated carbs after looking at the rubber ring they mount on...look OK..carbs secure. All controls smooth and move stop to stop.
Because engine SOMETIME ran well with top cowling off, we put it on and taped the oil filler door open to see if increased air flow would make any difference...it did not.
This is the third time the plane was just fine when put away and no good the following morning.
Temperatures have been moderate....high 40's at night, low 80's mid day.
Scat cooling from cowl to engine shroud secure and clear.
Pulling electric fuel pump fuse with engine running lowered fuel pressure slightly but made no difference in poor operation....nor does it make a difference with the engine is running well.
I am told that the definition of stupidity is doing the same thing over and over and expecting different results. I seem to be at that point now.
'Its still one giant mystery of intermittent good/bad operation.
John
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target="_blank" href="http://www.matronics.com/contribution">http://www======================
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[quote][b]
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rholder(at)avnet.co.uk
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| Posted: Fri Jun 08, 2012 11:07 am Post subject: Rotallxl 912 ULS Mystery |
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On 08/06/2012 19:42, JohnF wrote:
| Quote: | After a nice runup last evening; that is, nice mag drops
(about 100 on each side) and static rpm around 5050, and
engine running smoothing.
This morning I took the plane out to fly...taxi to end of
runway (about one mile) and did runup with oil temp
125-degrees F. Mag drop 330/360 - very untypical, and
running rough. Static impossible to reach. Engine rpm
decreased as throttle advanced past 4050 rpm or so....very
rough...idle way too low...around 800 rpm.
Experienced RV builder and local A&P got involved. We
tried all sorts of things; like removing the air
filters...no difference....sometimes, not always, if top
cowling was removed engine ran fine...sometimes not.
Nothing touches the cowl when it is on so nothing is
interfering with the engine due to cowl on or off. Only
air flow may be different.
Reseated carbs after looking at the rubber ring they mount
on...look OK..carbs secure. All controls smooth and move
stop to stop.
Because engine SOMETIME ran well with top cowling off, we
put it on and taped the oil filler door open to see if
increased air flow would make any difference...it did not.
This is the third time the plane was just fine when put
away and no good the following morning.
Temperatures have been moderate....high 40's at night, low
80's mid day.
Scat cooling from cowl to engine shroud secure and clear.
Pulling electric fuel pump fuse with engine running
lowered fuel pressure slightly but made no difference in
poor operation....nor does it make a difference with the
engine is running well.
I am told that the definition of stupidity is doing the
same thing over and over and expecting different results.
I seem to be at that point now.
'Its still one giant mystery of intermittent good/bad
operation.
John
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Idiot suggestion (idiot = me)
Have you checked that the plug leads are correctly
positioned and you haven't put a #1 plug cap on a #3 plug ?
Richard
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jacklockamy(at)comcast.ne
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| Posted: Fri Jun 08, 2012 3:35 pm Post subject: Rotallxl 912 ULS Mystery |
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Along that same line, I think the next thing I would try is a new spark
plug(s), pulling one at a time, check for hairline cracks around the
electrode and installing the 'new' plug in each position to hopefully
isolate the problem. Secondly, I would check my ignition wires, boots, etc.
I had a similar problem with a VW engine that had a hair-line crack in a
spark plug around the ceramic which could only been seen with a magnifying
glass. Cold engine would cause the crack in the plug to open up/fail. If I
got the engine running long enough to warm it, I guess the crack was closed
somewhat and the engine ran normal.
I hate it when engine problems are intermittent. Keep at it. You will
figure it out and we will have all learned something from sharing in your
experience.
Jack in Key West
--
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Dick Maddux
Joined: 24 Jun 2008
Posts: 516
Location: Milton, Fl
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| Posted: Sat Jun 09, 2012 5:17 am Post subject: Rotallxl 912 ULS Mystery |
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John,
I think you might find a bad plug if you 'bomb " test them But I thought I would offer up another fix I had to do on my engine.You have so little time on your engine I DOUBT this would be the problem but,who knows?
I too had an intermittent bad mag check (400 or more drop) that eventually worked into a dead mag on my engine a few years ago. After much testing, I finally checked the red power wire to the modules with an ohmmeter. I penetrated the shielding with a pin attached to one lead. (the other grounded) Working my way down the wire, I found a break in the core wire underneath the shielding that was sometimes making contact ,sometimes not.
After splicing the wire,my mag check returned to normal.
Ronnie Smith at South Miss Light Aircraft was a big help to me. I attended a couple of his Rotax courses.He knows these engines well ! You might check his brain also.
Dick Maddux
Milton Fl
912 UL
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Jim Feldmann
Joined: 01 Sep 2008
Posts: 54
Location: Burbank, CA
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| Posted: Sat Jun 09, 2012 8:12 am Post subject: Re: Rotallxl 912 ULS Mystery |
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I had a problem similar to yours one time after a carb rebuild. The enriching circuits (chokes) were installed backward. Either upside down or on the wrong carbs, I forget which. The result was that pulling the choke on made the mixture lean and the engine was hard to cold start. Pushing the choke off enriched the mixture and the engine would start to run very rich and exhibit the symptoms that you describe.
Installing the chokes in the right orientation solved all of the problems.
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Jim Feldmann
Kitfox IV Speedster / 912 lost to prop failure
Building a Kitfox 5 Voyager |
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