Mercury Tach correct

I am looking to buy a 2004 17 foot Lund Explorer with a 115 Optimax on it. We took it for a test drive the other day and at idle it is 1000 RPM. Listening to it seemed a little high but not really. At about 50 percent throttle we reached 6000 RPM and about 25MPH. We still had plenty of throttle left and at top end tach was pegged and we were doing about 40MPH. The motor does not sound like it has excessive RPM at top end. Guessing from the tach reading at 50 percent throttle if you trusted the tach there would have been about 9000 RPM at top end. Max for a optimax should be 5750 RPM. If the switch setting is incorrect on the tach I am guessing it would be proportionally off. I am on the right path or not? Any suggestions would be appreciated. I did check the prop and it appears to be the factory prop and does have a ding or two on it but nothing major.

Thanks

Re: Mercury Tach correct

Yes, it is likely that the switch setting on the back of the gauge is incorrectly set. The below thumbnail contains the specs for setting the switch.

Re: Mercury Tach correct

Thanks Chief. Getting the boat on Friday and hopefully will be able to fix it quickly.

r/
ETCS

Re: Mercury Tach correct

O.K. I got the boat and started doing some basic testing. When I turn the key to the on position the tach does change, however it only goes down to 600 RPM without starting the engine. I attempted adjusting the cal screw but the lowest I ever got it to was 600 RPM. I believe the Tach is shot and should get a new one. Any comments.

Thanks

Re: Mercury Tach correct

The gauge should go to zero when the key is turned on and the motor is not running. Since it does not, the gauge is probably bad. You might also retry this test while disonnecting the SEND wire from the back of the gauge. If the gauge then goes to ZERO with the wire disconnected, the gauge may be good and the send wire from the motor is causing a problem.

Check out the below link for more information on troubleshooting tachs.


http://www.downloadingfiles.co.uk/teleflexfiles/gauges/page342.pdf

Re: Mercury Tach correct

Thanks for the guide, I hopefully will have time to check it out this weekend.