Rpm gauge

planesailing

I think my rpm gauge under reads by about 500 rpm but occasionally it will read what I believe is the correct rpm (500 rpm higher than it normally reads). Any ideas how I can verify this and what's the best way to fix it so that it shows an accurate reading? The boat runs perfectly but this is one of the jobs on my winter "to do" list that I hope to sort out this week. Boat is 242 fiesta vee with a 5.7 efi merc and bravo 3.

Stodge

I'd try to lay hands on an external tach.  I have an automotive combination meter that does tach/dwell/volts/ohms and hook it to the coil to get a direct reading.

Check the back of the tach in the dash.  Many have a switch for 4/6/8 cyl.  Make sure it's still in the correct position.  Give it a few slides to loosen any gunk that may have formed in it.  Double check the connections on the tach.  Make sure they are tight and you have a good ground.

Good luck

planesailing

Thanks stodge. That's my job for tomorrow afternoon!

redlightning

if you have the faria gauges there is also a calibration adjustment aside from the 4/6/8 selector.  buy or borrow a meter you clamp on the coil wire and it will give you a digital read out of the rpm.  i let the motor warm up then made some minor adjustments to mine.   had to replace my dual tach cluster gauge with a rebuilt one and it was off from shipping.

redlightning

They are marked as :

STB HIGH is the  starboard high RPM fine tune

 

PH is the port high RPM fine tune

 

STB 0 is the starboard low RPM or 0 adjust (you should not have to touch this one if the tach zeros at key on).

 

PL is the port 0 or low RPM adjust (you should not have to touch this one if the tach zeros at key on).

 

PRT is the Port course adjust (set to 3 for 8 cylinder)

 

STB is the starboard course adjust (set to 3 for 8 cylinder)

redlightning

this info if for a dual tach.   hope this helps.

planesailing

Thanks redlighting. I have the older style gauges and only single tach. Will this have the same adjustment?

redlightning

I would think it can be calibrated.  I figured you didn't have the same but might be helpful.

Stodge

@redlightning it looks like you may have a Smartcraft Tach.  @planesailing I'm guessing you have an analogue tach.  Analogue will have fewer adjustments.  The cylinder setting on them is sometimes a slide style switch.

planesailing

@Stodge yes I have the original analogue gauges. Will hopefully get down to the boat over the weekend to have a look and will let you know how I get on.