rpm gauge inaccurate at higher rpms. 1991 johnson 140

[boating maniac]

Ok so i've had my boat for about 5 years and the voltage gauge has always stayed around 12 volts. I always charged the battery before I go out so I never really had a problem. So I think the charging system never worked correctly. Now on my last boat trip I noticed that at cruising speed the volt gauge will work it's way up from 12 to 14 volts after about 5 minute of cruising around 3500rpm. So now apparantly the charging system is working but once the volts go up to 14 the rpm gauge is off by about 1500-2000rpm. So it will show like 3000rpm on the gauge but the motor will sound more like 4500rpms. It only becomes inaccurate whenever the volts get up to 14. What's going on here?

 

[Will Bark]

Re: rpm gauge inaccurate at higher rpms. 1991 johnson 140

Sounds like dirty connections; check all connections on the back of the tach and volt guage make sure they are shiny and bright. Good luck

 

[boating maniac]

Re: rpm gauge inaccurate at higher rpms. 1991 johnson 140

Just to clarify the the rpm gauge has always been accurate until recently. I'll see if I can check the connections.

 

[boobie]

Re: rpm gauge inaccurate at higher rpms. 1991 johnson 140

It could also be a tach prob.

 

[V153]

Re: rpm gauge inaccurate at higher rpms. 1991 johnson 140

Sounds to me like your rectifier is headed south?

 

[boating maniac]

Re: rpm gauge inaccurate at higher rpms. 1991 johnson 140

Sounds to me like your rectifier is headed south?

The rpm gauge will quit completely if that happens then, right? I'm assuming my engine has a stator which is the alternator and the rectifier is the part that that tells the alternator when it needs to charge?

 

[V153]

Re: rpm gauge inaccurate at higher rpms. 1991 johnson 140

The rpm gauge will quit completely if that happens then, right? I'm assuming my engine has a stator which is the alternator and the rectifier is the part that that tells the alternator when it needs to charge?

I'm comparing your symptoms to a similar problem I had with an '86 motor. Sudden increase in battery voltage, erratic tach. Proved to be the rectumfrier. This is what I know ...

 

[boating maniac]

Re: rpm gauge inaccurate at higher rpms. 1991 johnson 140

I took the boat out this weekend and the voltage stayed right at 13 volts the whole time. The rpm gauge seemed to stay accurate too. Then again I didn't go too much past 3500rpm which is usually when it will do it. So I don't know maybe after all this time the rectifier wasn't working right or something. Atleast it charging the battery now cause before the battery would get kinda low and sometimes the starter would just free wheel and not engage onto the flywheel the first time.

 

[trendsetter240]

Re: rpm gauge inaccurate at higher rpms. 1991 johnson 140

I'm with the first poster. Sounds like bad wiring & connections.

FYI the rectifier is supposed to charge the battery up to 14.2 volts.