Tach Reading High

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BiteTime

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Thanks agian for the help with my last (and first) post. Those who saw it will know I bought an 1986 17' Sea Nymph with a Suzuki DT140 of the same vintage a few weeks ago. I have had boats before but this is my first outboard. <br /><br />The tach is a bit twitchy and (I hope) reading high. It tracks up with throttle but goes off the scale (6000 rpm) at around 2/3 to 3/4ths throttle. The boat may be underpropped with a 13x19 3 blade (original Suzuki aluminium - V1900 I think), but I get around 50mph flat out so I'm thinking it's not too far out.<br /><br />Does anyone have any ideas?<br /><br />I have a stainless prop, Suzuki VS1900 3x13x19 (i.e. same as the alloy one). What should I expect if this is installed?<br /><br />Thanks for the help.
 
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DJ

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Re: Tach Reading High

BitTime,<br /><br />You want the Suzy DT-140 to run about 5800 WOT. The 13X19 should be pretty close. I would suspect the tach. The engine has a rev. limiter that If I remember right is about 6200.
 
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BiteTime

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Re: Tach Reading High

Sorry, my request is not clear.<br /><br />I believe the tach or sensor to be faulty and am looking for advice about what to check before buying a new tach.<br /><br />I have some knowledge of electronics (that sounds dangerous :D ) and would pull the tach apart if it was faulty.
 
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petryshyn

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Re: Tach Reading High

>What Brand of tach?<br />>Any switches or calibration adjustments on the back?<br />>Does the tach climb smoothly, or is it jumpy?<br />>How is it at idle? What reading at idle?
 
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BiteTime

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Re: Tach Reading High

Hi Schematic,<br /><br />It is a Suzuki tach (same age as the rest of the boat).<br />I don't know if it has any jumpers but will check tonight (I am at work - it's 10:40am here).<br />These last two have really made me think. I may have to do a tank run tonight to check. I think it reads 0rpm at low idle (the engine runs a high idle for a few seconds after start - hot or cold). If I remember correctly, the tach reads erratically 500-1500 during the high idle. In gear it is steady from 4000up, but I can't recall what it is like below this in gear.
 
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BiteTime

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Re: Tach Reading High

I ran the motor in the tank last night and checked the requested areas. The tach reads smoothly above 900rpm and I now think the problem lies with the way the tach is set up. <br /><br />The tach and speedo are not Suzuki but Yuzuki brand (trim and water/oil warning are Suzuki). The tach has 3 inputs, one marked 'P', one marked '+', and one I believe to be ground.<br /><br />It also has a hole with a small slot screw. The screw can be rotated through 360 deg and (while its pretty sloppy) seems to be a 6 position switch. There are markings on the case for 2 of the 6 positions, these are marked '2' and '6'. There is a switch position between 2 and 6.<br /><br />When I saw this I thought 'problem solved' as I assumed that the unmarked position would be for a 4 cylinder motor and the switch had moved.<br /><br />But when I ran the motor at a high idle to get a steady 1000rpm indicated, this was the lowest reading that could be achieved by moving the switch. As I moved it around with the motor running it gave readings of 1000, 2000 and 6000rpm. The readings repeat for the last 3 switch positions. The 1000 rpm reading is given when the switch is at the '6' position and 6000 at the '2' position.<br /><br />Can anyone tell me if this tach supports a 4 cylinder motor and, if so, how to set it up?
 
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petryshyn

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Re: Tach Reading High

>Odds are good the switch refers to the number of poles. Your motor has 6 poles (12 winding poles/2) so you should be on the 6 position. The tack doesn't care how many cylinders, only the number of poles.It actually registers the alternator frequency, not ignition.<br />>Do you have a digital multi-meter with frequency capability?
 
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BiteTime

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Re: Tach Reading High

Thanks Schematic,<br /><br />I really appreciate the advice. I don't think my meter will do frequency, but I'll check tonight. I can get hold of an oscilloscope.
 
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BiteTime

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Re: Tach Reading High

Hi Schematic,<br /><br />My meter hasn't got frequency, but I should be able to work it out using a scope. Can you advise what I should be getting?<br /><br />Thanks,<br />Greg
 
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petryshyn

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Re: Tach Reading High

Hello BT:<br />If you connect directly to the tach terminal to ground, you'll probably see pulsating D/C (pending on Suzuki's wiring) You should get 6 pulses per engine revolution. The scope measures in milliseconds per division.(you have to set this)<br /><br />eg.<br />1000rpm X 6 pulses per rev. = 6000 pulses per minute<br /><br />6000 pulses per minute / 60 seconds = 100 pulses per second<br /><br />100 pulses per second = 10 pulses per 100 milliseconds<br /><br />"In a nutshell, count the number of pulses in 100 milliseconds and multiply by 100"<br /><br />Good counting!! :)
 
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BiteTime

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Re: Tach Reading High

Problem fixed :) - thanks for the help.<br /><br />I ran out of time last week and couldn't troubleshoot with the scope, but used the boat over the weekend. The tach worked fine! The power and signal connectors seemed ok when I had checked them so I guess the problem was fixed when I rotated the switch that selects the number of poles.
 
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