Yamaha RPM

[Larry]

I have a Yamaha 115 4 stroke on a 2012 2275 gcw. Purchased in 2013, motor ran at 5600 rpm WOT since purchased. The last few weeks motor runs normal for about 5 minutes then rpms start jumping up to 6800 but motor sounds no different and speed does not change. These measurements are on the factory installed tach. Anyone have any ideas what is causing this?

 

[Cwright]

Sounds like cavitation

 

[Lay Lake]

Could be a faulty tach Guage or a wiring issue. A loose wire can cause crazy things to happen. I would check the wires on the back of the tach to make sure they aren't loose or corroded.

 

[Larry]

Thanks will check it out this weekend

 

[Bill N]

There's a dial on the back side of your tach.
Note which position it's in, then rotate it back & forth full cycle leaving it in it's original location (thus freshening up the electrical connections).
Probably not the issue, but very quick, easy and free.

 

[sunedog]

If the motor doesn't sound different and the speed doesn't change, I am ruling out prop / cavitation / ventilation, etc. Sounds like a gauge problem or signal problem.

I'm no expert, but Google tells me modern tach's get their signal from the ECU and the ECU gets it from either a crank position sensor or a camshaft speed sensor.

Food for thought.

 

[Larry]

There's a dial on the back side of your tach.
Note which position it's in, then rotate it back & forth full cycle leaving it in it's original location (thus freshening up the electrical connections).
Probably not the issue, but very quick, easy and free.

Thanks

 

[Larry]

If the motor doesn't sound different and the speed doesn't change, I am ruling out prop / cavitation / ventilation, etc. Sounds like a gauge problem or signal problem.

I'm no expert, but Google tells me modern tach's get their signal from the ECU and the ECU gets it from either a crank position sensor or a camshaft speed sensor.

Food for thought.

Thanks

Thanks

thanks

 

[JohnL]

Although I have a different Yamaha motor, the tach does the same thing. It is a tach problem. I connected the engine information to my Garmin so I can watch the RPM’s and the reading on the Garmin stayed steady as the tach went up and fell back down. It’s to the point I don’t even bother with the instrument tach, I just use the Garmin.

 

[Larry]

Although I have a different Yamaha motor, the tach does the same thing. It is a tach problem. I connected the engine information to my Garmin so I can watch the RPM’s and the reading on the Garmin stayed steady as the tach went up and fell back down. It’s to the point I don’t even bother with the instrument tach, I just use the Garmin.

Thanks

 

[basshawk84]

My tach acts up like that now and again also.

 

[Larry]

My tach acts up like that now and again also.

Thanks