Tachometer races high

[excalibur-oc]

I have a 175 johnson sea horse that i have had for a while. This season I am having a problem with the tach showing the RPM's extremely high. At WOT it buries the needle. No change in speed, or the motor sound.

Any ideas on what is happening

 

[excalibur-oc]

Re: Tachometer races high

I am hoping a little more information may help.
My 175 horse J is an '84 - that is what the gentleman that sold me the B&M told me.
It is my first, so I am extremely cautious & do what I can to look after it.
After a rebuild a new prop, 2 inline filters & new spark plugs every year i had it running beautifully.
Up until mid this season, the RPM's were 5500 - 5800 WOT, the top speed, trimmed, on the 19' wellcraft airslot (HEAVY BOAT) was 38mph by GPS.
Now the RPM's are 2ble+ what they used to be.
At idle - 1800, they were below 1000
1/2 - 3/4 throttle gets me 6000 RPM & over
WOT now buries the needle on the tach.
The motor does not sound to be over reving & my speed has not changed.
However I am a newby when it comes to outboards & I am paranoid to run it.
I stumbled across 2-3yr old forum threads on the web search & found that there were some very knowlegable people willing to share their wisdom.
So I decided to register - could not find any archives with others having this issue.

Signed _ "landlocked"

 

[emdsapmgr]

Re: Tachometer races high

Post the model number of your engine. They did not make a 175 in 1984. Will help if we know the year.. Possible that your rectifier is going bad. When that happens, the tach starts to be erratic and read incorrectly. Also, the stator will no longer charge the battery. You should not incur any damage to anything running it this way, but may find a dead battery at some point unless you resolve this issue.

 

[farginicehole]

Re: Tachometer races high

I'm just subscribing to this thread as I'm curious to see what you find out. My '89 XP150 does something very similar. Sometimes it appears to be reading correctly, then all of the sudden it will jump up to 8000 or so rpm at WOT or 1500-1800 at idle with no change in the sound of the motor. Other times the needle will drop to zero for a few seconds. I sort of suspect a bad ground or connection somewhere, but haven't dug into it real deep yet. Good luck!

 

[excalibur-oc]

Re: Tachometer races high

Thanks em,
I will post thr #'s tonight when I get home.
I will also check the battery voltage standing & with the engine running to see if I have a charge.

ex

 

[excalibur-oc]

Re: Tachometer races high

OK here are the #'s
Model # J175TLCIH
Serial # J5516O21

I havenot checked the voltage across the battery yet - just got home

 

[emdsapmgr]

Re: Tachometer races high

Your engine is an 81. If the rectifier is not charging, you will need P/N 583408, about $58. This provides charging to the battery all the time- unlike the 89 XP, above, which uses the more expensive rectifier/regulator, and will cut back charging when the battery is charged. Erratic tachs are symptoms of problems with both types.

 

[excalibur-oc]

Re: Tachometer races high

I have just completed the voltage meter test
I have 12.7 volts across the battery terminals standing.

Idling the engine in the driveway, with muffs the voltage marginally increased to 13.2

Is that good or not so good?

 

[Tom Scully]

Re: Tachometer races high

That is about as good as it gets.
Was the tach acting up while you were taking the running voltage reading?

 

[excalibur-oc]

Re: Tachometer races high

Yes it was
The Tach was reading well over 2500 rpm.
I increased throttle to see if voltage would increase & the rPM's went to 4500 with a slite lift on the throttle.
No change in voltage

 

[Tom Scully]

Re: Tachometer races high

Those voltage readings are on the money, It sounds like an issue with the tach. Check the back of the tach, there should be a small "dial" type switch, make sure that the switch makes good contact in all it stop positions. You will be able to tell if it feels sloppy or not. It should be set for 6 pole operation, (#6 on the switch).

 

[excalibur-oc]

Re: Tachometer races high

Well I am glad to here something is on the mark.
I went out, located the smail dial on the back of the tach.
I knew I should of hinged the dash when i re did my interior, crawling up underneath it is a pain.
I could see 2,3,4 & 6 on the outside of the dial. The pointer was at the 6. With a small slothead I turned the dial back & forth betweem the 2 & 6 about 4 times. I would not say it was sloppy, it did turn freely, however there was no change in resistance at the # on the dial ie no click or hesitation, it did not feel any tighter at the # locations & i felt no friction.
That's the best way I can describe

 

[excalibur-oc]

Re: Tachometer races high

looks like you nailed it Scully.
After posting my last reply I went out hooked up the ole faithfull muffs.
Bump started the key & after 1 backfire????? I have no idea what caused that.
She started up & purred at 1000 rpm, lifted the throttle a bit it took her to 2000rpm.

Now that sounds like I have bad contact behind that dial/pulse switch.
Should i be looking at replacing that tach soon?

I am going to make the voltage check 1 of my prelaunch checks from now on to keep an eye on the recifier so when it does go I'm not manually trolling back one day because of a dead battery.

I can't thank everyone enough i only wish i had of found yous a few years ago.