well i took the isv (i think thats wot it is, a funny tube thing on top of rocker with two hoses coming out of it and an electrical connecter at one end)anyway sprayed a load of carb clener in it and the stuff that came out was as black as black can be, after abt half a can it started coming out clear, so fitted it back on started slug back up and job done, no more rev dropping although she is running a bit rough still, time for tune up i think