Shortened the chain and it works perfectly now.
All finished and yesterday I went for a test ride.
A lot better than expected!
It glides smoothly and shifts beautifully.
Even the brakes with cheap pads are great!
Thanks everyone for your help!
Here are some pictures
I'm pleased to report that despite an initial rejection, my 12yo boy tried the bike and loves it, especially the gears that on his existing ones are the revoshift.
I now need to get rid of his old one because I have too many bikes.
Anyone for a carrera 14" CTT?