Hey guys, just putting my bike back together (it's a European 1G1 model) and I thought the tachometer didn't work. I tried the old trick of hooking an electric drill up to an old cable I had and it worked....

Clockwise that is (which makes sense as the needle sweeps clockwise) BUT the cable from the engine is spinning counter-clockwise!!!

Have I put something back wrong?

I hesitate to answer questions like this...

Every Yamaha Tach I've ever seen... if you're facing the back of the gauge the cable needs to spin counter-clockwise. Drill would need to be a reversible type in reverse.

In any case, there is nothing you can assemble backwards or wrong in the tach drive. Unless engine is running backwards, the tach cable will spin the correct direction.

Things I can think of are that the cable is somehow not engaged properly in the drive or gauge... or cable core is broken and stops spinning with any bit of load or bend...

Oh and the reason I hesitate to answer is because direction of rotation can get confusing. It depends on which way you are facing.

(Similar to how the right and left side of the bike can get confusing which is why common convention is right and left is defined as sitting on the bike facing forward like you're riding.)

Anyway... hope answer helps... again, nothing can be assembled wrong to cause the tach cable to spin backwards.

Umm, motor running backwards. Don't laugh, i've seen it happen. Wouldn't happen on a cdi model though. So back to the drawing board.

So let's start by saying the bike rides as expected, i.e. not 30mph up the road in reverse Also, it runs on points, not CDI.

When I say clockwise / counter-clockwise I'm talking about being sat on the bike with the tachometer off and looking down the tacho cable. Needle sweeps clockwise from this position and, I assume, so should the cable.

I do have a drill that rotates either way and that's how I discovered the tachometer only registers in one direction.

This is why I hesitated to respond... I still think there's a disconnect on how the cable is being looked at.

When tach works with drill on end of cable, do you have it set on forward or reverse? (Forward is the normal drilling position or driving a screw in... reverse would be for removing a screw.)

Or maybe you can post a video to YouTube and link it here?

Okay, I'll keep it simple: I have the drill/engine end and the tachometer end. For the tachometer to work I look at the tacho cable top-down from the view point as if the tachometer was attached and then just moved out of the way.

From this viewpoint the cable looks to be rotating clockwise - in the direction you would expect the needle to sweep.

Sat on the bike, looking from the same viewpoint the cable is rotating counter-clockwise.

I did take a video but it's not clear at first glance what way the cable is rotating... until I slowed it down to quarter speed. I dunno how to do that for YouTube

Indulge me: if I asked you how to get the tacho cable to rotate the opposite way on a DT175 from the '70s how would you do it?

If there is enough room, with the cable connected to the tacho, disconnect it from the engine and attach that cable end to the drill. Double check that the cable is fully engaged in the tacho and spin the drill in the anti clockwise setting and hopefully it will work!

As MarkT said, the inner cable might be breaking down under load or maybe not fully engaging at one end.

Another possibility is that it is the wrong cable and the inner isn't long enough to engage in both ends at the same time.

Good luck!

With all due respect I don't see how cable length, quality or engagement can reverse rotational direction.

Request: if anyone has this bike or something similar (76/77 DT100/125/175) could you just unscrew your tacho cable, eyeball the direction it goes round and tell me whether I've gone completely insane Thanx!

I have more than one 175... early CT series through the DT175's... twinshock and monoshock. The tach drives are basically the same design on all.. a plastic spur gear driven off the crank with a worm gear that drives the tach cable. There's no way I can see to assemble it "wrong" where it would work at all much less rotate backwards.

Plus I've worked on countless 175's and if it was possible to mess up the assembly I would have done it by now...

My 1976 is probably the closest to your 1G0... tach cable spins clockwise looking down at it from top with tach removed. Same on all my Yamaha's from 1969 to 81... every model.

You're convinced it's rotating backwards...

I can't see how that's possible (without engine running backwards)... so as I said I think it must be a cable issue where it's not engaging (I've seen stretched outer housings) or internally broken.

I really can't argue with you about the rotation. You're there and we're not. I don't know how to help you either.

Maybe remove the cable from the engine end and drive it with your drill with the tach attached?

(You've never answered the forward or reverse question about the drill... drill needs to be on "reverse".)