Why did tacho go mental?
 

Having now put my bike back together after my off at Brands I took it out for a spin on Saturday afternoon with a mate of mine. My battery was pretty flat, even after charging it for the afternoon, so we had to give the bike a bump start. It still wouldn't fire up even then so another hour on the charger, another bump start and it eventually decided to play ball :)

Anyway, when it initially started the rev counter was going nuts. Shooting randomly up to 7k on tickover and right off the scale with only a whiff of throttle.

But after leaving the bike ticking over for about 10 minutes the rev counter returned to normal, and worked fine for the rest of the day. Was it something to do with the low power in the battery? Or will the rev counter go nuts again and need replacing?

I've had this and it was very simple to fix - the battery connections are loose!

They may not feel loose, but if you rock the battery tray (or the reg/rec bolted underneath) you'll probably get sparks from the earth lead as the connections make/break contact.

You simply need to tighten the connections up and it disappears.

It only happens when the bike is running as the revs causes the battery tray to wobble and the sparks cause the erratic behaviour.

Mine happened when I connected the Optimate lead and obviously didn't tighten it up enough.

Hope this helps!

Antonye hit the nail on the head with that, had this myself not that long ago on my 996, also seemed to be running a bit rough, turned out to be the negative terminal on the battery was loose, quick tighten and hey presto back to normal.

Cheers guys, I'll check it out when I get home.

Hey, thanks guys...
 

My tacho is also a law unto itself.

Sometimes it sits at zero when the engine is ticking over and most of the time just sits there flicking around between 4-5K regardless of what the revs are. It sometimes 'improves' when I give it a fistful.

The loose battery would explain it. My tacho has only gone mental since I sent the bike down the road on it's right hand side at Rockingham. That would've loosened the nuts...I know it loosened mine. ;)

I only spotted mine because it was the day after I fitted the Optimate and it had never done it before.

When I looked at the battery connections they seemed fine and tight, but wiggling the reg/rec underneath the tray caused sparks on the earth, so it obviously wasn't tight enough.

I thought this may be the case as I had an RGV250 that showed similar problems and I tracked that down to a bad earth too - one of the connectors was exposed to the elements under the seat. Replacing it and making sure it was nicely sealed cured it.

I'm sure it must be something to do with the vibrations of the bike that simply shakes things loose... that and throwing it down the road :lol:

You sure it's only the battery that's loose :lol:. Throwing a Duke down the road would seem to suggest otherwise.
And Jools I really don't think we want to know about your nuts mate...............;)

John