My '75 Cordoba leaves a tiny amount of black carbon on the driveway when the engine is started cold. My carburetor is not running rich either and the idle is fine. Should I replace the original muffler?
over the 3 years I've owned it, I've given it tune ups, done the timing a few times, adjusted the carb, even replaced the timing chain and no matter what, I get black blobs from the muffler. it practially disappeared until recently, but it has been very cold (like 45 degrees) when starting. so I guess we both learned something new!
Think about the condensation when the exhaust cools. Then that water gets pushed out when you fire up the engine and it picks up the loose carbon particles along the pipe as it exits. Once the exhaust is warm, it becomes vaporized and is spread out in the atmosphere.