Most likely you had the engine set too lean. An engine with a too lean setting will run richer when throttled back slightly, in fact it is a well known technique to experienced flyiers that if they get up with a lean setting to throttle back until they can land and readjust the needle. Most flyiers can't needle engines very well, as most set for maximum rpm on the ground and are cooking their engines in the air. When you take off, the prop unloads in the air (the prop is partly stalled on the ground). With the higher rpm in the air, the engine needs slightly more fuel, an leans out slightly.

The best way to set the engine on the ground is to run it up to full throttle, then quickly pinch and release the fuel line. The engine should pick up rpm with the quick pinch test. If it sags, then you are already too lean. This assumes the following, that the tank is located correctly, muffler pressure is attached to the tank, and that the engine bolts are all snug. Also be aware that you may be running too much load on the engine - either too high a pitch or diameter or both. For a newer engine stay at the lower end of recommended prop sizes until you have run at least a gallon of fuel. Alway use the pinch test at the start of each day.

Another thing that can also leave a black streak is if the muffler is loose. When two aluminum part rub, the particles are so small that it looks black in the oil. Which if you are runing too lean comes from your piston.