I have been driving my car ( original engine) quite a bit and keep noticing a significant amount of black soot ( carbon I suspect ) on the driveway at the tail pipe. The engine is running smooth, no smoking, little oil usage, but its beginning to worry me because the soot persists and the oil is a very dirty black, even though it has less than 200 miles since oil change. The car is making about 11 miles/gal and I suspect it should be doing much better. The plugs are also showing evidence of "dirty" combustion with some carbon build up. The car seems to be OK on power, but I have not yet checked compression. Since replacing the head gasket, I have been burning regular unleaded gasoline. Should I be adding a lead additive? Does anyone have suggestions as to the problem and possible things to do first.... like adding a bit of diesel fuel to the gas tank, other gas/oil additive, something thru the carb. etc.
Thanks in Advance
Don