when I start her up the temp gauge needle rises nicely up and gets to 90 without a problem. then after a time the needle rises and when a blip the throttle the temp gauge moves like the tacho? then if I put the NC30 into gear (from neutral ) and begin to ride off the temp needle falls. I don't really know what the temp is. does the fan rely on temp gauge to come on? I have checked fan and it does work. any ideas?

That is usually a sign of a bad earth - so check them and make sure they are all nice and clean and also the bolts are nipped up.

thanks where am I likely to find the earths?

Mainly under your feets!

Seriously though, don't feed it after midnight and keep it away from water, it'll be 'reet

I'm not really helping am I

the one causing this can be in the clock bracket or on the coil pack on the left front...

checked the earth on the clocks and the one on the frame near front coil. undid the bolts and sanded connectors. put back on but still temp gauge variable. the light switch also makes the temp gauge go up or down. at least the fan cuts in so hopefully no chance of overheating. turn the lights off and temp gauge drops, rev the bike and temp drops, put into first from neutral and temp drops??? weird

Would still suspect an earth problem. The green/black stripe wire from the temp gauge is the earth wire. Use a ohmmeter to check that it is a good earth and/or try tracing the wire through the loom to its earth point. If the Haynes manual is to be believed, this earth wire should go directly to some point on the frame.

prob with tracing the wire as the loom is wrapped in insulation tape with all the other wires. does anybody have any idea where the earth point on the frame might be?

you have one on the left hand side at the rough cast bit. You have one with the front coil. You have one on the front clock mount.

err.. there are more..

If the temp gauge sweeps - especially in relation to the electrical load..then it is an earth...