Coming back from work earlier on the A1 on my NC30 doing 75-80 and the bike decided it was going to mis-fire (I think) something terrible.

It bucked me about like a bastard and the rev counter was jumping between 1K and 3K even though I was still doing 70.

I pulled in on the left, luckily there was a layby quite close, and turned the lights off thinking it was draining the spark power.

I put the sidelights on as it was fine and got back onto the road well enough, using the revs up to about 10K then settled back down to 7K to cruise at 70 and it bucked me about a bit again and had to slow to 60 before it behaved properly.

Got off at the next junction and took it slow the rest of the way home and the bike behaved all the way, but I wasn't pushing it at all only revving to about 6-7K.

I know it's not fuel as the carbs are perfect, and I know its not air as the intake is completely standard. I have the speedo plugged in properly, so it's not the restriction thingy.

I've got to change the oil today and give the dirty girl a wash (using it everyday for work), is there any tests I can do to determine a cause?

Sounds like CDI if the rev counter was erratic.
Check the connectors under the seat unit.

Hmm shall check that, cheers

Some kind of electrical issue for sure.

Is the bike over-charging, as your probably aware this can easily kill an ignition box and cause similar issues.

I also had something very similar when the main fuse came loose.. dodgy electrical contact made haywire running

Just tested the charging, 12.7V bike off, 13.7 and rising whilst idling with no lights on, 14.1 and rising at 5K revs.

The connections to the CDI and starter solenoid were pretty clean, so was the fuse box with all fuses in good order. Gave it all a spray of contact cleaner just to be sure.

The connections to the coil packs are pretty dirty though so I'm going to wire brush them and get some contact cleaner on those too.

Will have to see how it behaves tomorrow or monday.

I'm getting a few things from Rick O soon, so I think I'll add the earth upgrade kit to the list.

Dirty ignition coil connections will not cause erratic tacho reading. Sounds more like battery over-voltage or intermittent loss of battery power to the ignition control unit.

If problem is worse at higher revs, ie higher alternator output, then may be start with battery over-voltage check.

magg wrote:Dirty ignition coil connections will not cause erratic tacho reading. Sounds more like battery over-voltage or intermittent loss of battery power to the ignition control unit.

If problem is worse at higher revs, ie higher alternator output, then may be start with battery over-voltage check.

Do the battery voltage readings I took in the last post not confirm the battery isn't over charging?

"14.1 and rising at 5K revs.", what about more than 5000rpm. You said the problem occurs when above 6-7000rpm.

Point well made, I'm not going to like revving it above 6k when in neutral though. Guess it'll have to be done.

Right just been and tested.

Battery voltage never went above 14.9 volts and I revved the bike to 10Krpm holding it for a few seconds to make sure the reading wasn't fluctuating. I revved the bike to 10K twice and both times never went above 14.9volts.