Tach needle bounced erratically

[Euroski]

Tach needle bounced erratically

I'm down to just a few left over bugs on my new to me Skater/ 300PM. The problem is the tach needle jumps down and up to where it was. I don't notice any drop in power or engine miss. My guess the drop is about 200-300rpm when in the 3000-4000rpm range. I'm sure it does it above that but I'm still breaking the engine in. The Livorsi tach is only about 3 months old. Any ideas on what to check?

[Riverratt]

Just a guess but did you check your grounds?

[skydog]

I am not sure but if the 300PM uses a rectifer like the 260 does that could be your problem. Guys??

Skydog

[supercat]

I don't know how similar they are, but I had tach problems on my 280's when I used certain spark plugs. Make sure they are the proper resistor type for the motor.

[Ziemer]

Check to make sure your battery is good and charged. Mine will do that when it gets a little low especially when I go up or down on the trim. Although I've got a 260 which doesn't put out the amperage like your promax.

[Euroski]

I checked all the wiring on the tach and engine grounds an all seems well. The tach is set to 12 pole. I did have the spark plugs gapped a bit tight, so will see what happens this Sunday.

[pyro]

Sometimes my tach will bounce or move erratically, and if I pound my fist on the dash it usually fixes it. :D

[Ron V]

When the first gauges went into boats, that's when worries started. Sometimes I wonder if you're better off not knowing what's going on since gauges don't work right anyway. Kind of like the way Greyhounds used to only have a speedometer so the driver wouldn't be distracted or worry about every little thing.

Seriously, check the connections to the gauges and to the battery first. A bad rectifier can make them dance. I had a 90 hp Evinrude that was making the tach dance; the rectifier was working fine but the signal circuit was bad. However, the tach will also dance if the rectifier is not working correctly so if checking the connections doesn't help then hook up a voltmeter with jumper wires right to the terminal board on the motor to rule out anything in the wiring up to the tach.

My tach drifted yesterday, first time it's done it with the new motor. Went about 300 rpm high and then came back down. Sometimes it just seems to happen. Interference, a fart crosswise, who knows. It's a 10 year old Faria tach.....I'm not losing sleep over it.

[Euroski]

Here's the fix for the wacly tachs, Livorsi has two different tachs. One made I think by them, and the other is a Autometer with Livorsi logos on them. I talked to ED at Livorsi and he was aware of issue especially on 300PM engines. They sent a Autometer tach and it works great! So the best thing to do is order the Autometer made tachs. Both tachs look very close to each other, but the autometer is written on the face in very fine print near the top.