I have a 2002 288 Sunsation I purchased this spring with 276 hrs when purchased and now I have almost 300 hrs on it as of now. I know the rpm's never seemed correct and I made a post asking if I had the correct prop which is 22 pitch bravo 1 and I'm running a 377 small block. I received a post back from a member stating my tach was incorrect. So today I used a infrared tach that I pointed at the harmonic balancer that I put a reflective tape strip that it reads off. This is what I got:


Boat-------- flywheel
1200------- 650
1600------- 1000
2000-------1700
3000-------2500
1200-------900

So my tach seems to be out as the forum member stated. Can the tach be fixed or should I be looking at buying a new one? I know some have setting for 4,6,8 cylinder engines on the back...could this be the problem? not being set correct. I'm unsure what to do from here as I would like to keep the tach as it matches the rest of the gauges.

As you can see in the above post I tested it at 1200 rpm twice and got two readings of 650 and 900 rpm. I'm thinking maybe a bad ground is possible. What do you think?

I had nothing but problems with my new Gaffrig tach. Same issue, it was all over the place when it worked. I replaced it with a Pro Comp marine that had the same face and rim color.

I wouldn't repair if you can live with the upgrade.

Turn the # of cylinder select back and forth a handful of times. Obviously put it back on the 8 cyl setting. See if that helps. If not, new tach time.

Guess I will take SB's advice first and if that don't work I will get a new pro comp marine as mentioned by TxHawk. Unless more options come up.

LOL.

I know, sounds weird, but it has fixed many tachs with issues like this, but not most. If you talk to a gauge company they'll usually tell you to try this first, before replacement.

As example here is what Teleflex says in a FAQ:
As analog tachometers age they sometimes begin to behave unpredictably and do not always display the correct RPM. Sometimes tapping on the glass brings the tachometer back to the correct reading…temporarily.
This abnormality may be caused by a thin film that grows between the Selector Switch contact and the circuit on the printed board. This film tends to intermittently insulate the two causing the strange readings.
To remedy this, simply rotate the switch about 6 times, resetting the switch to its original position. This should eliminate the film build up and all return to normal.
Erratic operation can also be the result of old age or a power surge (lightning for example) acting on the internal electronic components. This you can not remedy and the tachometer must be replaced.

its called the pole setting on the back of the Tach

also a guide from Faria

http://faria-instruments.com/site_ma...achometers.pdf

if applicable for what brand of tachs -- Pole Setting and it can be off a very small fraction of turn causing issues - so move it and turn it back in the correct slot. Actually this can fix tach problems, not all of them but a fair share amount.

http://www.pontoonboatforum.com/uplo..._setting_1.JPG

I couldn't find the different cyl settings on the back of this tach. So I just cleaned all connections and made sure things were all tight. I will see if that works, if not it will be new tach time!