The fart i suppose was, me thinking there was a wrong bell mouth in my kit, and me kept fiddling in the hope it would fit.....
Guess i should have left it alone for the next day
Apparently Carf uses this bell Mouth for multiple planes, and in one batch off Jokers they forgot to trim it back.
So there was the solution, cut it back about 5mm and now it fits perfectly.
Cheers,
Ed