Ok after breaking it a bit, got it sorted now. The misfire I developed at Brean off road course, was down to air being pulled in on the inlet manifolds, and I had ordered a Jet and rebuild kit from
http://www.shop.kaddieshack.com/ (highly recommended) in the US for the twin Kadrons and this all went in. Loads of crud in there too. All jets replaced and floats accelerator pumps etc.
To cure the rusting Ceramic situation ...
Goes like a scalded cat now so happy wife chap on the school run now.
