Tach error, 1987 Merc 4.3

[Evinrude Boater]

When towing a rider I'm used to running about 3000 rpm at 20 mph, at least that's what the gauges read. The last few times out when going the same speed the tach was at about 3800 and at WOT I seem to be getting 5200 rpm, usually it tops out at 4800. At an idle it seems to be the same as usual. I haven't done anything to the boat or prop to change the speed or operation. The boat has bottom paint so I doubt there's any marine growth. Could it be just a tach malfunction? I don't have another tach to compare with. I do have an old automotive analyzer that likely has a tach function. Maybe it will confirm.

 

[jerryjerry05]

Re: Tach error, 1987 Merc 4.3

Yea,put the anilizer on it and see the real results.It's an 87 and it's been around a lot of water.Moisture can affect the tach.J

 

[Evinrude Boater]

Re: Tach error, 1987 Merc 4.3

Hit a wave today and the tach came back a few hundred rpm. Tapped on the glass and it went back up. Sounds like a connection problem or faulty tach.