Tach or Alternator that is the question

[SlowOldGuy]

Pulling the fairing on a '93 is a piece of cake compared to getting it off of an '84/'85.  Just be careful not to drop the headlight.  You can pull the gauge cluster, and check that connector without removing the entire fairing.   But, it's not that much work to remove the whole thing.  That will give you easier access for checking/cleaning connectors and maybe tidy things up so they don't rattle around.

DavidR.

DavidR.

[RichBaker]

With mine, I'm pretty sure its the tach..... there's never been a change in the way the engine runs every time the tach has acted up.  I've got to replace the water pump in my van, then I plan to pull the tank and fairing and do some much needed maintenance. I'll double-check the wiring, install my DYNA coils and swap gauge clusters then..... I won't know which fixed it, but it SHOULD be fixed.

[racerrad8]

I recently purchased a 1993 FJ1200.  It's really a nice bike.  However, it did have a couple of problems. It wasn't charging correctly and the tach was reading double what it should.  I took it to the dealer as I'm not the greatest when it comes to motorcycle repairs.  The dealer put in a new voltage regulator that took care of the charging problem.  They indicated on the invoice that the tach was ok.   but, as I was riding home I notice that the tach was still doubling.   I took the bike for a 100 mile ride just to see what would happen, it ran great and at one point the tach actually settle down and read the correct RPM's for a short time.   When I call the dealer back that couldn't tell me if the tach runs off the alternator or the coil.   I actually called three different dealers and all were the same "clueless".  Can anyone out there give an old veteran some insight on this problem? 

The alternator system does not have any affect on the tachometer.

For some reason your tach is receiving the coil signal from both coils, when it should only be reading from one. I would hunt out the specific wire which looks like it is grey(gr) for the tach for your year model. That wire should run from the tach to the grey primary wire on one of the two coils. The other coil should have an orange wire. The other primary wire on each of the coils will be red with a white stripe. That is the power source to each coil.

There appears to be one connector in the loom, make sure corrosion has not allowed the circuit to be reading from the other coil. From there I would run a separate wire from the coil to the tach, eliminating the factory wiring.

There is a black (B) wire from the back of tach that appears to be the ground circuit for all of the gauges/lights.
The last wire is a brown (Br) that runs from the tach to the "resistor" the back to the "fuel pump control" relay. It is also part of the following circuits; Fuel Gauge, ABS warning and Neutral indicator lights. If those systems are functioning properly, you can probably move past that wire.

I would run the separate wire to the tach & coils first to eliminate try and eliminate the problem first.

I think if it was the CDI the engine would not know which coil was supposed to be firing at what time, and it would not run.

That is the diagnosis I would start with for the problem.

Randy - RPM

[thkfast]

Alright, everything is pretty much torn apart now.  I can see the grey wire come out of one of the coils, it goes into a white square plug, where it joins several other wires, then into a massive wrapped wiring harness where it T's off in all directions.  From the other end, at the gauges, I can clearly see 1 grey wire screwed into the bottom of the cluster all by itself and it's tight.  I started the bike and tapped, wiggled & played around with all the wires at the back of the cluster - no change in RPM.  Are you suggesting I cut the grey wire at the gauge cluster & coming out of the coil and temporarily splice in a section of wire to see what happens? 

[racerrad8]

Yep,

If the wire is screwed into the back of the gauge, remove that wire and insulate. Install a new wire that you can screw on the gauge and then run it down to the coil. cut it somewhere that you can install a connector and try that. My thoughts are if there is still the issues from there the tach is bad.

Randy - RPM

[thkfast]

CONCLUSION:

Okay.  I totally disassembled the fairing, gauge cluster, unscrewed the CDI - FULL ACCESS IN OTHER WORDS. Checked all possible connections - all look like new - unplugged, wiggled, re-pluged in.  The bike is naked.  Unscrewed the grey wire entering the bottom of the tach - started bike, no tach.  Fashioned a new jumper wire and crimped the appropriate end on it, screwed it into tach and connected the other end to the grey wire coming out of the right side coil just after the snap connector junction - started the bike, tach still reads double rpm's.  I'm assuming the CDI is fine because bike runs like a champ, there's apparently no shorts in the wiring loom going to the tach.  The needle isn't jumping around like crazy...just double the rpm.  Unless I missed something, I'll take some photos of it disassembled, then put her back together tomorrow.   

[racerrad8]

If the black ground wire also screws on the rear of the tach, make another ground to a new clean grounded connection and give that a try before you put it all back together. Just to cover the fact the ground wire to the tach could be bad.

Randy

[thkfast]

Randy,

Did as you suggested, unplugged the black wire on back of tach next to the grey wire - ran bike, of course no tach.  Then connected a jumper wire in same spot and grounded it to the frame and tach reads same high rpms.  The nice thing is I have total access to EVERYTHING right now.  Let me know if there's anything else you'd check.  Will hold off on reassembly a while.  Thanks!

[thkfast]

Here's where I tapped into the grey wire after the connector off one of the coils



Here's where the brown - black - grey wires power the tach



And finally the bare naked front end of the bike



The bike is now back together and tach still reads double rpms - I'll ride it awhile and see if it fixes itself...

[MyFirstNameIsPaul]

Hate to say I told you so, but, I told you so.

[SlowOldGuy]

From what you've done so far, I would have to conclude that a circuit in the tach has gone bad.  If it is reading exactly double, then it sounds like it must be counting the "wasted spark" event.  At this point, you probably need to replace the tach, unless you can find an electronics person that can locate and replace the bad component.

DavidR.

[thkfast]

Agreed.

Yeah yesterday I started the bike cold (it was about 78 degrees outside) required a little choke.  At first,
the rpms were READING CORRECTLY!  I thought OMG, it's fixed.  But by the time I rolled it off the center
stand and started down the street, I could see the rpms slowly rising to X2.  I tried it again just now cold
and it's doing the X2 thing.  eBay gauge clusters look pretty nasty - cracked and scratched $95-200 gamble.

I'll keep my eyes open for a decent gauge cluster...

Thanks guys!

[thkfast]

CONCLUSION:    I FIGURED OUT WHAT WAS WRONG WITH MY TACH!

It appears I wasn't riding it enough.  We had some crappy days, I had been driving the car more and neglecting the FJ12.  Once I resumed riding again, the tach started working intermitantly, then for the first 2 miles or so, then today it just started working right - period.  Now that was an easy lesson!

[Dan Filetti]

CONCLUSION:    I FIGURED OUT WHAT WAS WRONG WITH MY TACH!
It appears I wasn't riding it enough. 

The cure for oh, so many problems!

Hope it stays that way!

Dan

[RichBaker]

From what you've done so far, I would have to conclude that a circuit in the tach has gone bad.  If it is reading exactly double, then it sounds like it must be counting the "wasted spark" event.  At this point, you probably need to replace the tach, unless you can find an electronics person that can locate and replace the bad component.

DavidR.

It should be calibrated to count the wasted spark event...... these actually read the pulse train as a proportional voltage. All the tach is is a voltmeter, nothing fancy....

We're almost back to bearable temps here in Tucson, and I'll be doing some work on my '90. I'll swap out the guage cluster then and I plan to open up the tach and see what they're doing with it.