[Hell Driver]

Good point, look at the simple stuff before looking for more complicated answers! Today the leads, cap and rotor arm were changed, still not running right, 1 and 4 plugs still covered with carbon straight away with 2 and 3 staying clean. I put some injector cleaner in the petrol and as if by magic, plugs 1 and 4 once cleaned now stayed clean. (I also swapped them to middle positions to discount plug problems.) I also put in a gallon of fresh petrol on top of the one I put in a couple of weeks ago to dilute the old stuff in there (which was minimal). The engine was still running a bit rough at low revs, sounded better at higher revs but still not quite right. Also every so often it began hunting faster and slower. One thing I did notice was that the plug nearest the cam belt end was always wet (petrol) when I took them out. (maybe the engine always come to rest with injection of petrol on this cylinder?). As it's coming off anyway I decided to take the cat off. Now with the sensor off and no back pressure I assume the engine will not run correctly anyway! It appears to be no worse now, maybe the lambda sensor was not working anyway? The cat looks OK inside on the engine side.