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Old 27 May 2013, 11:44   #1
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Merc 15 misfire?

I have a 15hp mercury 4 stroke that's about 5 years old. It has always had a slight misfire when at full speed at WOT. This doesn't happen at WOT when accelerating or into a headwind i.e. when the engine is under a little more load.

Could this be a rev limiter kicking in or is it a genuine misfire? It is an audible intermittent "bing bing" noise in an otherwise smooth engine note.
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Old 27 May 2013, 13:29   #2
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Install an induction Tiny or Hardline tach and check max rpm achieved at wot with you alone preferably on flat calm waters. If passing 6k could be the cause; if counting with a rev limiter, it's doing his job.

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Old 27 May 2013, 14:38   #3
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Quote:
Originally Posted by Locozodiac View Post
Install an induction Tiny or Hardline tach and check max rpm achieved at wot with you alone preferably on flat calm waters. If passing 6k could be the cause; if counting with a rev limiter, it's doing his job.

Happy Boating
Thanks, is this something that can be done on a lift on/off outboard with no external wiring or controls?
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Old 27 May 2013, 17:36   #4
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Induction tachs are installed in/out engine, just wrapp several rounds of provided wire around plug wire, will need to program the firing sequence though for engine to read well rpm achieved. Just follow tach's installation procedures and you'll be fine.

Better yet, buy a hour/tach meter. Will record elapsed runing hours, perfect for preventive maintenences: leg oil, spark plug, valve adjustments, oil & filter changes. Hardline has a much friendlier installation, just one cable which can be cut to size after tach/engine final cable routing, while TT doesn't.

Happy Boating
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