oh ok.. oil in the exhaust... heres your solution..... use some form of oil absorber... sand, kitty litter, sawdust, and with the engine running at 4500 rpm where it occurs, dump a 5lb bag in slowly to the carburetor... as its going through your exhaust system itll grab any oil and shoot out the exhaust.... then your problem is solved! and make sure you get the stuff thats not gonna cause wear to the muffler bearing....