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Faulty tacho.

Discussion in 'Technical and Troubleshooting Torque' started by smiley235, Dec 23, 2007.

  1. ok, i've noticed as of late that my bike tacho has been continually bouncing up and down while im riding and idling, sometimes bouncing up and down across a span of 3,000rpm. Now this is annoying as hell. As an example of how random it is, I pulled up at the lights, no throttle and clutch pulled in. engine sounded like it normally would (i'm guesing between 1500 to 2500rpm), but my tacho was bouncing between 10,000 to 12,000rpm.

    Any1 know what would cause this? I dont wan't to change anything yet till i know why its doing this. If it makes any difference, by bike battery is completely flat and I have to roll start it (as in it wont even attempt to crank and it doesn't even have enough power to release the latch on my boot unless the bike is running). I've been sourcing out batteries but all the places are out of stock till the new year. bike is a suzuki across.


  2. your reg/rec is fudged, and is delivering a spastic amount of electricity to your instruments.
    the reg/rec chances the charge from your alternator from AC to DC and keeps it at a consistent voltage. if this isnt functioning proper, your instruments will be getting spikes of electricity, which could terminally damage them.
    this is only my guess though...
  3. shit, thats not good. My cars packed up on me and now this :(

    Where can I hook up my tester to the reg/rec to see what voltage its outputting?
  4. 1. start bike, let it idle.
    2. remove negative (earth) battery terminal, so you are measuring output voltage, not output + resistance from dead battery.
    3. test voltage between positive terminal (still connected to battery) and negative terminal (disconnected)

    report results.
    output should be between 14-18v

    remember, im just a bush-mechanic :LOL: i really am only guessing!
  5. That has a mechanical tacho, doesn't it? It's driven by a cable of the camshaft...I think. Easy to check, have a look at it!

    Usually when they bounce and are cable driven your cable is about to break, or just very dry. Remove it at the engine end and pull the inner cable out. Grease it verly lightly with petroleum jelly or water resistant grease, but very lightly!

    If it is electrically driven - no cable but electrical wires instead - the fluctuations can be due to a poor earth, or maybe even the lack of a battery to stabilise the alternator/rectifier and voltage regulator output. Get a new battery first if it is electronically driven.

    However, even electronic instruments still use a mechanical mechanism to rotate the needle and when this gets dry it can bounce around because of the high friction inside. In this case you will need to have it serviced professionally...

    Hope this helps

    Trevor G
  6. I'm pretty sure its an electrical tacho, i'll have to check it out.

    I did what you said joel but as I was removing the negative terminal, the engine started to conk out so I put it back on. It was measuring a steady 8v which is not good. When I stopped the bike and took the battery out, it was measuring 10V. So i chucked it onto this battery charger I made in tafe for about 3 hours. It now measured 12V. Put it back in the bike and now there was enough power to dimly light the neutral light but still not enough to crank, so i'm gonna change the battery in the new year and hopefully my tacho settles down after that.

    Thamks joel and trev
  7. thats what i hoped might happen.
    means the reg/rec isnt blasting out a bazillion volts, and that the massive voltage drop is caused by a fudged battery. the battery is placing a huge resistance in your charging system and that will cause your consistent voltage dependent instruments to act up,
    when you charge a 12v battery, it will read around 13.8v hot off the charger and drop to around 12.8v resting voltage.
    12v or less wouldnt be enough turn anything over.
    replace it when you can, and be sure to update us :)

    edit- if you are finding it hard to source a genuine battery, how about this http://au.geocities.com/ozcross250/battery-alt.html
  8. awesome joel, that makes good sense. I might even check out these other batteries too.

    Thanks heaps, i'll be back with the result.
  9. No Good Cam
    try a few places like battery stop in campbellfield - they will be open all days apart from public holidays and should have it on the shelf
    Battery world may also be able to help you, depending on the franchisee some are really good with keeping stock and some are shit!

    Good luck matey!
  10. whachoo talkin' bout willis?
    the suggested mod battery would work just fine.
    right V, enough CCA, a little fiddling and it will start no worries!
    but you are right, batteryworld and such should have a suitable repplacement for the OEM battery.
    all that matters as far as batteries is concerned is that it will-
    (a) have enough cold cranking amps to start the bugger
    (b) the ability to accept the charge from the alternator without cooking
    (c) fit in the battery box without too much mod's
    auto electrics is a very simple thing.
    even if the replacement battery has MORE CCA, no worries!
    on the other hand, if you are saying his predicament is no good....well, err, my bad :grin:
  11. thanks nick, i'll check those joints out soon. I might just stick with the oem battery to play it safe, as Murphy's law has a tendency to screw me around when I change things a bit.

    By the way, merry christmas every1 :)
  12. ok, back for an update. I hadn't mentioned but I stopped riding my bike after new years as it was getting harder to roll start, and the engine only felt like it had 30% power, was jerking everywhere and it would kept conking out whilst cruising along at say 60km/h. Then I would roll start again, and it would feel alright, then conk out again shortly.

    As far as I was concerned, I thought my bike was on its last legs. Well today, autobarn finally got the battery which I had been waiting for like 3 weeks. Put it in, was cranking beautifully but wouldn't start (I think cause old fuel+air in the lines) so roll started it. Let it warm up for 10 minutes.

    Then I took it for a spin, and it had 100% power!!!. All my lights were brighter, each gear revved without missing a beat, and also, my tacho is behaving normally now!! Can't believe how much of a difference it made. Well i'm sure the alternator is relieved to have a break. So i'm rapped and thankful for all the help given in this thread. :)

    On another note, I had to fill the battery up with acid myself with these dispensors that you put upside down in the battery and break their seals. Autobarn also said for some reason, the supplier sent me a big bottle of concentrated sulfuric acid (and I dont see how I would use this for batteries as they cant be opened again and the dispensors are safer and hold the right amount). Well, the autobarn guy was as confused about it as I was but I took it anyway.