Fitted my PTFE gasket today. Its the first time the inlet has been off since the engine was built 4000 miles ago.



I noticed that all 4 inlet ports were like this. Clean but with the black marking around the opening. Its not burnt on. Its like a oily substance (can't really smell anything at the moment which doesn't help!). Any ideas? Im going to clean it all off and whip the inlet off in a few hundred miles to have another look.
I did go through a stage of the car running badly. It kept on misfiring on two cylinders which was finally solved but i can't see this being the cause as i would expect it to be different between 1&4 and 2&3?