tach question

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   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.

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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 Topic: tach question 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.”

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 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

tach question

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