tried dizzy cap, rota arm, leads & plugs & still no joy

tried another fpr as had this problem before & was that but still no joy

looks like the heads cimeing off when i get back from offshore for further inspection!

does seem like a valve problem when its running rough but dont get how it can be when the next minute its running mint??

runs on 4 cylinders but badly on idel (sounds like its on 3)