Modern 4-stroke engines with modern fuels do not get excessive amounts of carbon on things anyway. I would not worry about it. Engines stripped after 100,000 miles show only small amounts of carbon. 2 -strokes on the other hand are a different story but modern synthetic 2-stroke oils and more effecient engines have reduced it a lot. You find carbon on the top of the piston, valves, cylinder head and exhaust ports but as I said with a 4cyl 4-stroke I wouldn't worry, most bikes will never see more than 50,000 miles in 20 years.