New digital tachometer on ‘78 Evinrude 85HP not working correctly

[Spreng]

Have a 1978 Evinrude 85HP (model 85899C) that I’ve been working on. Runs like a new engine, however I can’t get the tachometer to work correctly.

The boat (1978 Ray Craft V150) originally had an Aqua Meter two-wire tachometer which was in disrepair (physically broken). Replaced it with a generic digital tachometer (Geloo 85mm 6000 rpm on Amazon) but got no reading whatsoever. That, coupled with a battery that didn’t seem to get charged, led me to replace the rectifier.

After replacing the rectifier there is some activity on the tachometer but it isn’t at all accurate - upon initial start-up the needle will jump to 2,000 rpm, then a second later to 3,000 rpm, then a few seconds later it’ll peg at 6,000 rpm and remain there until the engine is shut off. During operation the needle is steady - no jumping or bouncing to indicated a loose connection somewhere.

There is good continuity between the gray signal wire at the tachometer and where it screws onto the terminal block by the rectifier. There is also good continuity between the ground at the tach and the battery. The instructions for the tach I bought aren’t the best, but I believe I have poles set correctly (they list a 6-pole outboard to be set at “3” via the digital readout of the tachometer, which is where I have it set). I also tried setting the tach to “6” via the readout but there was no change in behavior.

Does anyone have guidance of where to go from this point? The stator physically appears fine (no black tar-type gunk around it).

Thanks in advance!
Evan

 

[sam am I]

Sounds like just spurious noise that's added in with the speed signal, obviously equal parts noise and sig can jumble up the readings........Try adding (splicing in) some resistance (1-20K ohms) in series in the signal line, this will add some filtering that should reduce the higher freq noise and allow the lower freq signal to be greater of the two.

Use a 20K pot wired as a rheostat if you can, this would help tune it in easiest.

 

[GA_Boater]

When tachometer and motor pole questions come up, I always use the guide from Faria. Below is a snippet from the Faria manual;



I think you should use the 12 pole setting, not the 6 pole setting.

 

[Spreng]

Thanks for the suggestions. I’ll first try setting the tach to the 12 pole setting and if that doesn’t do the trick I’ll wire a pot in series with the gray signal wire, if I have one that’s around 20k (found 500k and 1m but may have others hiding around - I do have many different resistors that I can try rather than a potentiometer if it comes down to it).

 

[Spreng]

Changing the setting to 12 seems to have done the trick....mostly. The tachometer now reads approx. 650 RPM at idle. Once, the needle quickly climbed to 6000 RPM while engine was idling, hovered there for a few seconds, then dropped back down. A couple other times while idling the needle fluctuated between 2000 RPM and 500 RPM (no change in actual engine speed). The tach seems to react to changes in engine speed somewhat slowly but I suppose that could be normal behavior for a cheap electronic unit, or I’m just too used to automotive tachs that react almost instantly.

Read a steady 13.8V at the battery while idling.

 

[sam am I]

Nah, you still have noise issues........Unless defective, it should be stable (not 500 - 2K at idle) and react more or less instantaneously

 

[Spreng]

Nah, you still have noise issues........Unless defective, it should be stable (not 500 - 2K at idle) and react more or less instantaneously

It was stable at idle 90% of the time - definitely still an issue. I have a 500k pot laying around that I may put in series with the signal wire. Though it’s 500k I think it has a fine-enough adjustment that I can get relatively precise readings in the lower range. I’ll hook it up in series with the signal wire tomorrow and see what happens.

 

[Spreng]

Here’s a short video I shot today of the tach:

- YouTube

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[sam am I]

Here’s a short video I shot today of the tach:

- YouTube

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

www.youtube.com

Ahhhhh, yeah, that's not so bad, I'd live with that as long as it stays accurate through its full range.. Mine bumb's like that every once in a while.