mate, i dont think you have stated enough facts for anyone to help ya.

not had this problem myself after owning a couple, could be a misfire problem.

have u tried new leads plugs rotar arm dizzy cap?

seems strange that u have stage 3 head cossie turbo and all those mods on a standard chip?

send karl norris an email karl@norrismotorsport.co.uk and get it sorted properly.