I wonder if anyone can give me an idea of a couple of easy things to check first rather than cleaning the carbs.

I started my NC30 after several weeks & it only fired upon 2 cylinders, both front pipes are cold.

I only bought it 6 months ago but been assured this hasn't happened before as it's been extremely well looked after.

2 front cylinders dead would suggest ignition coil or LT supply to it.
Will it run OK on choke?
Rev the engine to see if the front 2 chime in at higher revs, if so carb pilot circuit could be blocked.

Possibly the plugs, but I have found they pack up one at a time, but remove them to check for spark anyway.