They said it was the diaphragm inside the metering head where the red fuel lines go into it,
Said it was split and they had a spare one,,

The garage used to tune rs's and cossie's back in the 90s
They're based in southend
That's why I went there as my tuner is in London and didn't want to break down on m25 lol
Thanks for your reply

Ok I'll try the yellow plug when I get home cheeRs