Four Stroke Engines: Why is there black carbon deposits on spark plug and black carbon out of the exhaust?
This is caused by to rich of a air/fuel mixture, weak ignition or wrong heat range spark plug (too cold). You might need to adjust your carburetor and lean out the air/fuel mixture first, also check that the choke is not partially stuck closed, or the float in the carb might also be stuck partially open which causes excessive fuel, also check for the correct spark plug. What is happening is all of the fuel in the combustion chamber is not being completely burned during ignition, this leaves hydorocarbons, that stick to the surfaces in the combustion chamber, spark plug, muffler, and goes out to the atmosphere which causes pollution. The most common cause is the carburetor. As a last resort if adjusting the mixture doesn’t work, remove the carb and disassemble it, clean it , reinstall it and readjust the the fuel mixture, this should solve the problem. John Follow up: Thanks for the help. It was the air cleaner. Strange because a brand new Honda 5.
