Tachometer doesn't work at low RPM

[cliff75]

Tachometer currently doesn't work at low RPM but originally wasn't working at all on my 1972 Evinrude v4 100hp (100293R) so I installed a new the tacho gauge setting it to 6 (from everything I've read what it's meant to be set at for this motor) but without success.

So then after doing some reading I tested the rectifier and replaced that after finding it faulty.

Now the Tacho started to work (kinda) but it won't read at low rpms eg. anything under about 1300 rpm the needle goes straight up to the max rpm of the gauge around 8k and then as you increase the revs the needle drops down to 1400 and then the gauge starts working as normal.

I thought there could have been some problem with the wiring (having some sort of resistance somewhere along the line) so a ran a new wire directly from the rectifier/stator connector to the back of the gauge but had the same result.

Just wondering what could be causing this problem and what I can do to fix it?

Just to note the charging system of the outboard seems to work eg I can see the volts slowly rise with the rpm eg. around 13V or so at 2k rpm


Thanks
Cliff

 

[boobie]

Do you have the correct tach for your motor ?? Is that your motor model # in your post ??

 

[cliff75]

I believe so, it's an aftermarket tacho which can be set to handle multiple different engine/stator configurations.

http://www.islandinflatables.com.au...ter-★-black-black-★-boat-marine-gauge-12v-24v

 

[joeanna]

Just a thought; do any/all other guages work correctly? do you have another known good tach to try?. When a rectifier isn't working, it may let AC current/surges get threw?

 

[cliff75]

All my other gauges work but I've only got a gps Speedo, voltmeter. No other working Tach to try

 

[cliff75]

All my other gauges work but I've only got a gps Speedo, voltmeter. No other working Tach to try.

 

[fhhuber]

Check the connections at all the rubber wiring boots under the engine cowl.

I had similar issue that slowly got worse then started having the tilt-trim not work. Turned out to be one of the connections not fully plugged in.

 

[cliff75]

I'll definitely double check all wiring on the engine there's not really that much on these old evinrude really

 

[oldboat1]

Not my cup of tea, but I think I recall a thread on pre-'77/'78 tach wiring -- Joe Reeves, I believe. (Can't find it at the moment.) But there is a tech memo on the Crowley site, and it might be useful: http://www.crowleymarine.com/support...meter-kit.html Check it for overall instructions, and also for a wiring change that might be needed (pulse switch setting and relocation of tach lead). The tach in question is a BRP Tech Series tachometer | 0174983