tach question

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   Larry - Let's turn this into a generic troubleshooting the tach thread since my tach is reading in error as well.  

I assume we should start at the engine and work to the dash.  My old tach has cylinder settings and a trim pot on the back to fine tune the rpm.  So, I figure we need to go to the source and cut out the wiring harness to begin with.  How do we do that?

I have this crazy laser rpm gauge for lathes... would sighting that at the crankshaft pulley give me engine RPM as shown on the tach?  Can I try to trim the tach to those points at varying RPM?  Should I pull the tach out of the dash and go straight to the engine with it?

What's the best way to zero in a tach?

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Air206 Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Grand Poobah Joined: September-28-2008 Location: Roanoke, VA Status: Offline Points: 3000	Post Options Post Reply Quote Air206 Report Post Thanks(0) Quote Reply Topic: tach question Posted: August-08-2013 at 6:09pm
	Larry - Let's turn this into a generic troubleshooting the tach thread since my tach is reading in error as well. I assume we should start at the engine and work to the dash. My old tach has cylinder settings and a trim pot on the back to fine tune the rpm. So, I figure we need to go to the source and cut out the wiring harness to begin with. How do we do that? I have this crazy laser rpm gauge for lathes... would sighting that at the crankshaft pulley give me engine RPM as shown on the tach? Can I try to trim the tach to those points at varying RPM? Should I pull the tach out of the dash and go straight to the engine with it? What's the best way to zero in a tach?
	04 Air206 91 Barefoot 78 SkiTiq

75 Tique Members Profile Send Private Message Find Members Posts Visit Members Homepage Add to Buddy List Grand Poobah Joined: August-12-2004 Location: Seven Lakes, NC Status: Offline Points: 6130	Post Options Post Reply Quote 75 Tique Report Post Thanks(0) Quote Reply Posted: August-08-2013 at 2:03pm
	My tach shows roughly 500 to 700 RPM high, I would guess (based on rule of thumb that 1:1 trans and 13 inch prop, then MPH ~ RPM.)(note speeds are GPS speeds, so I am confident in those) I will also point out that at top-ish end, it always seems off. At lower end (like idling) sometimes it seems right (600-700)and other times it seems to read high (1100, when I know its making 600-700 sound) Before I drop the dough on a new tach, are there other possible causes of this symptom? (wiring, ground.....?) or do those symptoms suggest the unit is the culprit? Thoughts? Thanks.
	_____________ “So, how was your weekend?” “Well, let me see…sun burn, stiff neck, screwed up back, assorted aches and pains….yup, my weekend was great, thanks for asking.”

tach question

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