Tach - not reading correctly at WOT

Hi

Similar issue to a recent post about Tach. Mine is not stuck - it just seems to read to high around WOT. It is a Faria Tach on a Four Winns Horizon 180. I have read a lot about giving them a thump/rap - I also read about moving the switch on the back of the tach between the various positions - from 4, 6, 8 - I assume to clean the points.

I went to the boat had a quick look and cannot see the back of the dashboard when I look up lying underneath the dashboard (i.e cannot see the the guage, when I look up - I see loads of wires).

A few questions :

1) to access the Tach do I need to disconnect all the wiring and unscrew the Dashboard and lift out
2) Assuimg 1 is correct - is there anything I should be especially careful of when disconnecting the wiring?
3) Is it worth worrying about - it reads about 800/1000 rpm too high. I am assuming the engine is fine.

Thanks

Andrew

Re: Tach - not reading correctly at WOT

How do you know it's reading too high? It could be the engine is over revving.

Re: Tach - not reading correctly at WOT

andrewnzinuk said:

I also read about moving the switch on the back of the tach between the various positions - from 4, 6, 8 - I assume to clean the points.

Click to expand...

Actually that is to correspond with the number of engine cyls

Let's back up a second. What are the actual numbers you are getting that tell you too high? What RPM, at what speed (GPS) and what pitch prop? Do you know your gear ratio? You may be dead right (that it's wrong), but this will help all of us help confirm it. I may move this to a different section depending on your answers. This is more than likely nothing to do with the engine or drive which is what we would usually post in this section.

Edit: simul . . .

Re: Tach - not reading correctly at WOT

Hi Don

How can you tell if motor is over revving?

Thanks

Andrew

Re: Tach - not reading correctly at WOT

andrewnzinuk said:

Hi Don

How can you tell if motor is over revving?

Thanks

Andrew

Click to expand...

If the rpms show over the WOT spec for your engine, then it's over revving. But then you have to determine if the engine is actually over revving or the tach is wrong. Personally, I can hear 1000 rpm difference, and if it's over normal WOT rpm and sounds like it, then it's time to find an accurate shop tach to verify the boat tach.
If they show the same, then you have other problems.

Re: Tach - not reading correctly at WOT

andrewnzinuk said:

Hi Don

How can you tell if motor is over revving?

Thanks

Andrew

Click to expand...

That's what the tach is for. If the manufacturers recommended WOT rpm is 4400 - 4800 rpm and the tach is reading higher than that one of two things is going on: 1) the engine is indeed over reving or 2) the tach is indeed wrong. So we are back at the original question: What makes you think the tach is reading wrong and that engine is NOT overreving? If the engine is idling properly and the tach shows about 600 RPM then it is highly unlikely the tach is wrong at the high end.

Re: Tach - not reading correctly at WOT

If the boat is out of the water, pull the tach and send it to Faria to be rebuilt. It'll cost you a few bucks but you will have a new tach that works correctly and it will take out the guesswork for you. Don't overrev your engine because that is why you will be buying a new engine in short order.
Here's the website link for Faria:
https://faria-instruments.com/forms/?form=new

Re: Tach - not reading correctly at WOT

I don't care who touches it, or rebuilds it, if the switch is set wrong, the indicated RPM will be wrong . . . I am not sure why anybody recommends sending it out if we are still trying to ascertain whether it is reading correctly as is.

Re: Tach - not reading correctly at WOT

Sorry there QC, I did not mention to check if the setting is correct on the back. Start there. If it does not help when verified with a shop tach, send it in.

Re: Tach - not reading correctly at WOT

All good. Sorry I may have sounded short. Just wanted to get back on track. I don't think the OP has been back though . . .

In order if the OP returns:

1) confirm tach reading
2) If wrong, check switch in back
3) If switch right, tach is junk . . .

If tach is reading right, it's time to discuss propellers.

I guess you could reverse 1 and 2.