If it ran up to 10krpm without misfiring, perhaps an intermittent connection in the ignition control unit wiring (battery feed or earth return). Also check the run/stop switch as it feeds power to the ignition system, battery and main fuse connections.

Just took the bike for a run as I found out it's going to rain later.

It worked perfect under hard acceleration, held 90mph comfortably and didn't seem like anything was wrong.

I'm going to use the ignition wiring diagram on this: http://www.akhara.com/nc30/nc30manuals/ ... 0R_C15.pdf

How would I check for an intermittent connection at the ICU? Surely if it's intermittent it'll be a pig to find?

YES! Particularly if it only occurs when out riding. All you can do is check the wiring and connections for the ignition system, battery power feed and rect/reg. Note an intermittent battery connection will cause a complete loss of electrical power, the charging system will not compensate and keep the bike running as the rect/reg output will be zero.

Right, plenty of wiring to check then.

I ordered one of these last week as I've always been paranoid about my electrics, because they seem fucked....

http://www.ebay.co.uk/itm/261204574843? ... 1497.l2649

I shall get that fitted when it comes, then at least I'll be able to monitor the battery voltage on the move.