Rpm

[marauder11]

Ok first question i have a 120 hp 1986 outboard. I have a 17 pitch prop on it what is the rpms i should be getting at wide open throttle. I got it up to about 35 mph. I know that speed depends on boat passanger ect. My RPM gauge was all over the place up to like 5.5k down o 1k . With my old 19 pitch prop i was getting around 5k RPMs So next question can i just buy a replacement gauge and hook the two wires up to it . Please help

 

[arthurj12]

Re: Rpm

when tack is acting funny its your rectifier on its way out happened to me and my dads . i have a 90hp v4 and it has a 15 pitch prop it goes 5.1k hope this helps

 

[Solittle]

Re: Rpm

5.5k for that engine is great.

 

[marauder11]

Re: Rpm

rectifier is that in the rpm gauge or ?. Also have only charged battery once at the start of season have been out at least 10 times and have never had a power issue with motor starts ups ect. Total time on water is close to 25 hours.

 

[marauder11]

Re: Rpm

ok after reading some other stuff here i think i figured it out. The tach has to be the issue. The battery has keeped a charge for the whole season just off the boat running. So my rectifier has to be working to charge the battery. My tach is original 1974 to the boat. The local boat shop also agrred that if i had no loose connections and the tack was working most the year so far that it will most likley be the tack.

 

[woody66912]

Re: Rpm

I think that you should at least do a volt test at the battery to see if you 14.4 volts. If you do than it is most likely your tach. With your old tach installed literally bang it with your hand, if it jumps around than it's your tach.

 

[marauder11]

Re: Rpm

I think that you should at least do a volt test at the battery to see if you 14.4 volts. If you do than it is most likely your tach. With your old tach installed literally bang it with your hand, if it jumps around than it's your tach.

With motor running or just sitting in driveway

 

[woody66912]

Re: Rpm

With motor running or just sitting in driveway

Engine running.

 

[boobie]

Re: Rpm

Sounds like a bad tach.

 

[marauder11]

Re: Rpm

Engine running.

Ok i had to run and buy muffs.Could not find my third set lol. Anyways i let the motor idle in the driveway for about 4 mins. Rpm gauge was noy jumpy and was at about 2000 rpm. Voltage was at 13.7 to 13.9 volts dc from the battery post. So not sure if this is a sign that rectifier is going or if this is an ok voltage. Model number of motor is cj120tlcdc.

 

[marauder11]

Re: Rpm

Anyone know if 13.7 is ok reading? Do i need to remove the fly wheel on my motor to get this replaced .

 

[marauder11]

Re: Rpm

Boat shop close in 1 hour anyone have an opinion on the 13.7 volts at the battery. Is this ok or should i be changing out the rectifier.

 

[boobie]

Re: Rpm

Sounds okay..........to me.