Tach problems

[savage454]

I got my bike running better but now I'm having a problem with my Tach. At an idle I can rap the throttle and it will go up pretty fast on the tach, when I'm riding the tach goes to about 3 grand sometimes 3500 and that's it, although the engine is obviously reving higher. I pulled over and took the tappet cover off and oil flung all over so I believe my pump is working. What could cause this? Dirty cable? Pinched?

75, pods w stock jetting, and open exhaust. New pilot and main on the way.

 

[xjwmx]

I had that happen once for some unknown reason after I had the tach off and put it back on. It eventually fixed itself. The only thing that drives the needle is magnetic influence, no direct connection, so it doesn't take much friction to do that. If it doesn't clean itself and work right in a month or so, then maybe oil the needle with the tiniest amount of water-weight oil. I suggest not pulling the pointer off the needle.

 

[savage454]

Okay cool thanks. I had heard somewhere the tach is ran by the oil pump and if the tach stops working the pump does. The tach works it just jumps around and isn't going past 3500 while riding. I cleaned the cable, I'll see what happens.

 

[xjwmx]

That sounds like what mine was doing.

The bottom of the cable is driven off the same gear as the oil pump, so therefore if the tach stops moving the gear that drives the oil pump might not be moving.

At the top end of the cable there's a magnet that the cable spins and it makes the needle that the pointer is on deflect an amount that depends on its speed or rotation. No physical linkage from the cable to the needle at the top, just magnets.

 

[savage454]

Okay, so are you saying that the problem might be at the tachometer itself? With the cable off I started the motor and it was spinning at the case. Maybe my magnets are getting weak or they're dirty or whatever? One of the screws that hold the face plate on the tach is out and just jumping around under the glass and the other one is getting much looser. I read a couple threads on here about fixing that, maybe it has something to do with that.

 

[xjwmx]

Okay, so are you saying that the problem might be at the tachometer itself? With the cable off I started the motor and it was spinning at the case. Maybe my magnets are getting weak or they're dirty or whatever? One of the screws that hold the face plate on the tach is out and just jumping around under the glass and the other one is getting much looser. I read a couple threads on here about fixing that, maybe it has something to do with that.

I'm sure the problem is with the tach itself.

The magnets aren't weak, the needle the pointer is on is being pressed on, either by dirt or loose grease, or....

I think you might be onto something with the loose tach face. If the hole in the face was touching the needle, that would cause what you're seeing.

I took the glass off my speedometer to put a screw back in the face. The tach opens the same way. Look for 650skull's thread on taking the bezel and the glass off using a bent screwdriver. That's how I did it.

 

[savage454]

Cool thanks mang.

 

[XSLeo]

When you put the screws back in, be careful too snug cracks the face.
When snugged up a drop of nail polish will lock the screws.
Leo

 

[savage454]

Okay thanks, I was thinking about that earlier while riding to work and cursing my gauges.

 

[Okie]

I'm curious, do other Yamaha tachs work the same way? Will an XS750 tach work on a n XS 650?

 

[XSLeo]

Some will hook on and read ok, others may not. The red line will be at the wrong rpm.
Leo

 

[72XS2]

If you open your tach, don't forget to use blue loctite on the screws. This way, they won't come loose again.