Hi All,
Went out for a ride with my other half on her NC30, Mine was fine but hers decided to play silly buggers.

Half way through our ride she said hers went onto 2/3 cylinders. We headed for home slowly until it cut out completely. Would try and fire but wouldn't start, applying any throttle killed it.
Called the AA... and waited 30mins. They called saying there was nobody in the area so tried her bike again and it fired on all four, so off like a flash heading for home. About another mile in it started to miss and went onto 2/3 cylinders until grinding to a halt.
Repeated this process to get it home allowing 10mins to cool between break downs.

Has anyone had anything like this before? To me it sounds more electrical? As if some things breaking down when fully hot.

Bikes never been a problem up to now I've checked the tank breather valve and that's fine.

Don't think it is electrical, if 2/3 cylinders failed then all 4, what would cause that?
CDI 2 or 4, coils/pickup 2, plugs/leads/cap 1. If a connector came loose it may misfire then stop but it would not start again.

Sounds like fuel, so check the tap diaphragm and the vacuum hose to see if perished or cracked.
Take a look at the tank breather hose too.
What has been touched recently,

The carbs should not refill with engine not running, but still worth a look.

Recently I've lifted the needles 0.5mm and drilled the slides as per HRC mod. It's covered a good few miles since then though... maybe 150/200.

The tank breather is ok, I blew down it after a quick search on here before I posted.

I will check the tap and vaccum hose over the weekend

I would replace the vacuum hose regardless, you can't always tell if it has 'collapsing' issues by inspecting it.

It might also pay to do some basic electrical checks on the bike too, only because faults are common, can manifest themselves in all sorts of running issues and they don't take long to do. All you need is a simple multimeter - every nc30 owner should have one!

Was the bike on reserve or main?

Check fuel flows full bore from the tap outlet.
Remove hose and place a bowl/tray/cup under the outlet.
With engine stop switch set to STOP, and fuel tap set to ON, spin the engine on the starter for 2 seconds to observe flow.

A low flow may be diaphragm punctured or less common blocked filter or blockage within the tap body.
Check/replace vacuum hose first.

Thanks I'll try the above, the problem was the same in the on position OR reserve. I tried both...

The tank breather could be kinked causing the tank to become air locked.