I have a 1980 280E euro with 4 speed transmission and there is exhaust smell coming from engine when I am driving with windows down. I opened the hood and noticed that the strong smell comes from exhaust manifold area and is probably carbon build up (because it smells like it). The engine sounds normal and smooth with plenty of power. Fuel pressure and fuel mixture has been adjusted recently by a good mechanic. Would that smell be related to insufficient combustion in the cylinders or just the excessive carbon build up? Also if the manifold gaskets were leaking wouldn't it be loud and noticeable?
If it is the combustion what could be the cause, fuel injectors, ignition, etc? Also if there was no leak how does the smell come out so strong? When I bought the car 7 months ago fuel pressure was out of wack and the mixture was way too rich so I suspect maybe faulty fuel injectors. The car runs really good except for that smell which is pretty annoying.
Any input would be greatly appreciated,

Thanks,
Harvey