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The ECM is the engine control module. It controls various engine functions such as spark timing which it changes depending on the position of the gear position switch and the air jet solenoids of which I know little. It is possible to test their function, the Clymer and Honda service manuals spell out some checks on these units. Unfortunately I don't know all that much about them because I haven't had to dig into them yet. The spark plugs being black adn the hesitation and dying when advancing the throttle could be caused by a leak in the carbs, a sticking CV valve, or a problem in one of the many vacuum hoses, a possibly a problem with the reed valves, etc. There are many possible causes and the only way I know to determine what is causing it would be to check out the various systems by checking the components according to the service manual(s).
