So I'll try keep this as short as possible... Nc30 was running perfectly, didn't use it for maybe six weeks or so, come to use it again, starts up straight away, then dies 30-45 seconds later... It then won't start up again until I come back to it the next day... I've tried it multiple times and same result again and again... What I've 'diagnosed' so far...

Fuel-
Fresh fuel
Checked fuel tap, pipes, all good
Carbs clean- full with fuel when I took them off once it died...

Electrics
Battery, Recently new, good charge
Spark plugs good condition, little wet with fuel after it dies
Ht leads seem good, pulled both rear caps off, stuck old plugs in to check spark after died, all good...

Everything else generally looks good... Any advice would be greatly appreciated or if anyone knows/does mechanics that can come out (just outside north London) that would be great!

Does the fuel tank have a vacuum line like the rvf??

Make sure that's all secure because if its not it will run off the fuel in the bowls but then die..

All the pipes are secure, have double checked it too many times!... Really can't understand what's causing it...

Anyone know of any good mobile mechanics or anyone on here with a good knowledge of nc's that could help?

You pull the out fully and the engine starts and runs for 30 secs and then stalls?

I'm guessing the word you missed to be choke?...

I can get it off choke and even keep it running for a short time by revving it but it still eventually dies on me...
I've started it at least ten times or more and the same thing has happened, so have tried plenty of ways to keep it running but same thing happens

Yes, "choke" was missing. Does fuel flow freely from tap when vacuum is applied to the hose, also try running the engine with the fuel tank cap open, in case there is a blockage in the breather hose.

So I managed to run the bike yesterday, had the fuel cap open, it ran for a bit longer, maybe a minute and a half or so.
Got it off choke and kept it running for a bit by revving it, as soon as i stopped revving, it idled for a couple seconds then died and wouldn't start again...

It seems to be smoking from the exhaust when running, a lot more than it usually did also... Don't know if that would give any indication of an issue?...

You did not say if fuel flows readily when a vacuum is applied to the fuel tap.

How can I test that?... I took the tank off the bike and fuel flowed fine into a bucket... (tank cap closed)

How many hoses connect to your fuel tap. I may be mistaken but thought NC35 would have vacuum operated fuel tap and thus two hoses, one fuel, the other vacuum.