dirty petrol in tank flled up with good petrol several times since, engine running a bit rought wtat can i do?

Answer 1

Did you also change the fuel filter? Not knowing make and year of vehicle is difficult to make suggestions, as depends if carburator or fuel injected engine. May try running some fuel system cleaner through a full tank of petrol.

Answer 2

keep changing the filters and run injector cleaner every tank , your carb. or injectors may need to be re-done if it won't clear up after 4 or 5 more tanks