hi i have a 1975 CB550F. ive noticed that the bottom two exhaust pipes are showing alot of carbon on the outside. i would like to know why, and how to fix this please. the top two pipes are fine. i shd probably add that the bike is one hundred percent original, with no known major work done on it, apart from the head gasket is leaking a little ( wouldnt be a honda aye ). the bike has done 34,000 miles. ive had the tappets and valves clearance done a fews weeks ago. i thought it was a fuel problem, so the carbs got cleaned, ive had the bike for 10yrs, and am not a winter rider, i guess age is starting to show( mine not the bikes).