tachometer reading @1000 revs too high

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    Posted: 19 Aug 2014 at 9:54pm
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Hi everyone, can someone tell me why my tacho in the boat has a reading of @1000rpm even when the engine is off, and then climbs from there? So total revs when running are approx 1000rpm over what they should be? Does it need adjusting to zero or something similar or hasnt it been wired correctly? Engine is elpto merc with factory guages. cheers
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Post Options Post Options   Likes (0) Likes(0)   Quote flyfisher Quote  Post ReplyReply Direct Link To This Post Posted: 19 Aug 2014 at 9:55pm
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There should be a setting (dial with slotted head) on the back for 'poles' 2p, 4p, 6p, 8p etc. What is it currently set on and what is your engine hp and config 2 or 4 stroke?
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Post Options Post Options   Likes (0) Likes(0)   Quote fishwpa Quote  Post ReplyReply Direct Link To This Post Posted: 19 Aug 2014 at 10:36pm
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mine is the same - would like to know as well. I will check my setting tomorrow for my Merc 60hp 4 stroke.
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Originally posted by fishwpa fishwpa wrote:

mine is the same - would like to know as well. I will check my setting tomorrow for my Merc 60hp 4 stroke.
Also have Merc 60hp 2 stroke and tacho sits on 1000 when motor off. Seems to read ok when running though so haven't given too much thought to it until I saw this. Will be interested to see how this pans out.

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Post Options Post Options   Likes (0) Likes(0)   Quote flyfisher Quote  Post ReplyReply Direct Link To This Post Posted: 19 Aug 2014 at 11:15pm
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On many tachs if you turn the motor off, the last recorded RPM will be displayed on the tacho (i.e. for me, usually about 800rpm as that is what the motor is doing when I turn the key off for the day) - this is normal I believe, cranking again or key to ON, should clear it back to zero.
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Post Options Post Options   Likes (1) Likes(1)   Quote MacSkipper Quote  Post ReplyReply Direct Link To This Post Posted: 20 Aug 2014 at 12:23am
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I have spent a bit of time on these Tachos as I got thru several used ones before buying new and that failed after a while - bummer!. Mercury Tacho on older motors (mine 2006 2 stroke) is very basic old design - has a switchable selector for number of cylinders - if wrong will give numbers right out if at all. Your selector will be correct if setup from new. Tacho sits on a thousand rpm or so power off, power on (key on) then shows zero and reads revs when motor running. When stuffed often first sign is power off reading stays high or lower than 1000rpm (have seen both), actual speed reading is adjustable by a pot thru slot in back and affects rpm reading by a lot mainly at top end - can try setting to idle 1000rpm or so (higher rpm small motor, lower rpm big motor) but accurate way is to check against another tacho and adjust at WOT (is fun try adjusting a small pot in back of tacho flat out - need a calm day) - I have an optical tachometer and can adjust accurately by flashing a dot stuck on flywheel - not a good idea in rough conditions! If stuffed buy aftermarket a lot cheaper I have bought a kus new from trade me can get in black with combined hour meter - same size hole and a fraction of OEM mercury price. Cheers
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Simplest way to check your tacho reading is on trade me for around $36  are small sealed digital tachos.... feed the wire into the engine and wind the end 3 or 4 times around a plug HT lead.
These are also programmed to set service time engine hrs etc
instructions in the box

they are accurate have tested against the  'dyno on tarmac' data logger in the chevy
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Good point steps about those small tachos - I forgot about those is a cheap and easy way of checking accuracy.
I did not go for one of them as I have a big hole in my dash where previous tacho was and wanted same size to fill, also I like looking at a dial.
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Post Options Post Options   Likes (0) Likes(0)   Quote funandfunction Quote  Post ReplyReply Direct Link To This Post Posted: 20 Aug 2014 at 7:16pm
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The 2p,4p,6p,8p switch on the back of the tach can get a bit of corrosion on the contacts and make the tach over or under read. Rapidly switching backwards and forwards for 15 seconds or so can sort the problem.
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Post Options Post Options   Likes (0) Likes(0)   Quote Polar_Kiwis Quote  Post ReplyReply Direct Link To This Post Posted: 20 Aug 2014 at 8:49pm
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Originally posted by funandfunction funandfunction wrote:

The 2p,4p,6p,8p switch on the back of the tach can get a bit of corrosion on the contacts and make the tach over or under read. Rapidly switching backwards and forwards for 15 seconds or so can sort the problem.

I also have a 60hp Merc efi. Sometimes it seems to over read while at say 4000 rpm. Maybe by 500-1000rpm. Do you think this could be the problem or something else?

Cheers


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Post Options Post Options   Likes (0) Likes(0)   Quote the angler Quote  Post ReplyReply Direct Link To This Post Posted: 20 Aug 2014 at 9:37pm
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Originally posted by Steps Steps wrote:

Simplest way to check your tacho reading is on trade me for around $36  are small sealed digital tachos.... feed the wire into the engine and wind the end 3 or 4 times around a plug HT lead.
These are also programmed to set service time engine hrs etc
instructions in the box

they are accurate have tested against the  'dyno on tarmac' data logger in the chevy


Hey would these work on a diesel inboard ? And what's a ht lead?
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Post Options Post Options   Likes (0) Likes(0)   Quote Olfart Quote  Post ReplyReply Direct Link To This Post Posted: 20 Aug 2014 at 10:40pm
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Mike .... An HT lead is any one of the spark plug leads on your outboard.  
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Post Options Post Options   Likes (0) Likes(0)   Quote the angler Quote  Post ReplyReply Direct Link To This Post Posted: 20 Aug 2014 at 10:56pm
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Oh , no good for me then I have neither...
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Post Options Post Options   Likes (0) Likes(0)   Quote funandfunction Quote  Post ReplyReply Direct Link To This Post Posted: 21 Aug 2014 at 2:12pm
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Originally posted by Polar_Kiwis Polar_Kiwis wrote:

Originally posted by funandfunction funandfunction wrote:

The 2p,4p,6p,8p switch on the back of the tach can get a bit of corrosion on the contacts and make the tach over or under read. Rapidly switching backwards and forwards for 15 seconds or so can sort the problem.


I also have a 60hp Merc efi. Sometimes it seems to over read while at say 4000 rpm. Maybe by 500-1000rpm. Do you think this could be the problem or something else?

Cheers




I learnt the above from a Mercury mechanic who did it to my tach and fixed the problem. If you've got the older style gauge , have a look on the back.... think nothing to loose. Don't think this applies to the Smartcraft gauges.
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Post Options Post Options   Likes (0) Likes(0)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 21 Aug 2014 at 3:59pm
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I have also seen some advertised on TM that uses a sensor and a small magnet on the fly wheel.  No idea how good they are.

Originally posted by the angler the angler wrote:

Oh , no good for me then I have neither...
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