Carbon on the port side of valves often indicates oil leakage around the stem- worn guides or stem seals. Carbon on the spark plugs can result from either oil consumption or rich fuel mixture, depending on whether the carbon is dry and powdery (fuel mixture), or heavy and kind of caked on the plug (oil consumption). If the plugs are the wrong heat range (too cold), you will get the carbon on the plugs. If they are the heat range specified for normal operation, there is more to be discovered. If you can post a picture of the spark plugs, that would help considerably.
Heavy carbon in the combustion chamber usually results from ring leakage, but worn valve guides are a possibility also. At this point, there is more to your story.
Harvester
