There is oil in the fuel no matter if there is a smoke trail or not. The so called smoke trail is actually unburned fuel, not oil. If the glow plug is too hot you will have a considerable smoke trail even when the engine is set too lean. This is because you have to richen up the mixture to quench the plug so that the timing is retarded. If the glow plug heat range is right you will only have a slight smoke trail at a rich setting. So a smoke trail is a poor way of determining if the mixture is correct.

Get a tach. And wear ear plugs. Even with today's mufflers they can do damage to your hearing.