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stabelvej9(at)gmail.com
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 Posted: Sun Sep 16, 2012 6:10 am Post subject: 914 - rough running, and RPM drop when testing the A circuit |
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Hi
Today I had a 800 RPM drop and a rough running engine on my 914 on the A ignition circuit (top spark plugs), when making pre-flight check.
All wires and spark plug connectors seems OK on a visual check.
Did not bring the "big" toolbox to the airfield today.
Any suggestions were to begin troubleshooting?
Best regards
Gert Dalgaard
OY-GDS / Mono / 915 / 500 hours
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rampil
Joined: 04 May 2007
Posts: 870
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| Posted: Wed Sep 19, 2012 6:32 am Post subject: Re: 914 - rough running, and RPM drop when testing the A cir |
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First, the check for the spark plug harness is not really visual, but a feel.
Actually a yank of at least 7 lbs to disengage the connector from the
plug. I have seen loose connections several times including on my 912s.
Next pull the top plugs for a visual and electrical inspection (ohm meter).
After that I would consider carb issues.
Good luck,
Ira
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kees de bussy
Joined: 16 Jul 2009
Posts: 18
Location: the netherlands
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| Posted: Fri Sep 21, 2012 2:44 am Post subject: Re: 914 - rough running, and RPM drop when testing the A cir |
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For what it is worth. I experienced 2 times a similar problem with my Rotax 912s. About 4 years ago for the first time and it was figured out that 1 of the wires of 1 of the ignition boxes was broken close to the connector. The wire was soldered which solved the problem.
A few weeks ago it happened again. So I checked the wires but with no result. Furthermore I checked the spark plug leads, spark plug connectors, pull off force, etc. replaced all the spark plugs but no results.
Eventually the problem was located by a local Rotax dealer who discovered a faulty ignition coil. The error in the ignition coil could not be detected by measurement but only by swapping parts. Hence it was a real pain to find out.
Good luck.
Kees de Bussy
PH-SBR
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budyerly(at)msn.com
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| Posted: Sun Sep 23, 2012 12:49 pm Post subject: 914 - rough running, and RPM drop when testing the A circuit |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Kees
Had the same experience. Good ohm check of the coil, but after buying two coils and swapping them around, finally found the bad one. Tell tale sign was the steel plates that make up the core had corroded and began to split a bit at the edge. Autopsy revealed the inside was worse. I guess the distance of the split of only a fraction of a mm reduced the coils effectiveness. Found a second coil with corrosion and changed it out also.
We also used a timing light on each plug wire looking for weak spark or a miss, and that was somewhat effective finding it also. Very frustrating to do though, as the proximity of the pickup to the plug and direction of the pickup must be the same on each cylinder to get results that are conclusive.
Bottom line is it is a bit of trial and error. Not for the impatient or those of limited means. It takes a bit of time.
Regards,
Bud Yerly
Tech Support
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