Cuts out on one cylinder after 10 min.

[Blacktrain11]

They are new plugs but I did as you suggested and swapped them, but still the same result.

 

[Bertrrr]

This is a confusing issue, Makes no sense - Lets assume it's Not fire - now you will need to concentrate on fuel delivery , pump- filter- carb . You never say never in mechanical issues and cannot get too focused on one thing.
I've learned this the hard way. Looking back on your post I see you've checked the fuel system as well.
If it were me, I'd hook up a new fuel source with an electric fuel pump and see if anything changes
I ran into something like this and found my fuel line was sucking air - only figured it out after using an electric pump hooked up to a gallon bucket of fresh fuel , you never know.

 

[bertsmobile1]

As the saying goes
When you have eliminated all of the possible then only the improbable is left
On a twin cylinder with a single barrel carb when you have ruled out electrical you are left with fuel
And on your engine it can only be a leak at the inlet manifold ( there is a rubber seal there ) or a bad valve / cam lobe
A loose valve guide can cause random stumbles