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John Herbert
Joined: 05 Oct 2007
Posts: 6
Location: South Africa
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 Posted: Sun Apr 04, 2010 3:44 am Post subject: Unusual Tach indications |
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I have just completed a re-build of a Kitfox IV with a 912 UL engine and standard Rotax tach for a 912. After the re-build (with a new fuselage), the tach reads normally only above 2200 rpm. Below this it suddenly jumps approx 1000 rpm higher. I have checked the reading with an external tach and the are correct for revs above 2200. Troubleshooting has been to check ground continuity to the engine and the general electrical connections on the engine. If I disconnect the ground wire on the tach, the Tacho reads smoothly throughout the rev range, but under-reads by about 300 rpm.
I have not yet checked for dirt or corrosion under the tacho pick-up yet, thatis my next job, otherwise any suggestions?
John
Tel. 00 27 834634865
Fax. 00 27 865285196
P O Box 879
White River
1240
South Africa
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Roger Lee
Joined: 10 Jan 2006
Posts: 1464
Location: Tucson, Az.
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| Posted: Sun Apr 04, 2010 3:42 pm Post subject: Re: Unusual Tach indications |
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Hi John,
You might try a completely new ground. Just make it temporary to just check it out. Your other ground may be a ground, but may be a very poor ground.
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_________________
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056 |
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ami(at)mcfadyean.freeserv
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| Posted: Mon Apr 05, 2010 4:41 am Post subject: Unusual Tach indications |
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Oft quoted:
Rotax produce a guide to tacho problems which is available on line.
One of the solutions suggested is to solder a 100 or 200 ohm resistor across
the trigger coil (or tach) terminals.
Duncan McF.
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