QuestionI find some times my bike won't idle very well but is fine when I rev it up today I am having a no spark issue from 1 coil last season I replaced both coils and have only about 2000 km on them
the bike was fine last week and now wont idle .I am kind of confused how can I bench test the coils, and which direction should I go to back trace my problem , I am fairly good at turning wrench and not to bad with my meter just need some direction thanks Don
AnswerDon.... "won't idle very well" could be any number of things. Is it firing on all cylinders at idle or dropping one set? Have you had the carbs off for cleaning and inspection of the air cut valve? Is your charging system working? DOHC Honda fours have a history of weak charging systems, usually due to bad rotors.
You have to start with the basics.... Check compression on all four cylinders. Should be around 175 psi, throttle held wide open. If you have low cylinders, either it needs a valve adjustment or some engine repair work.
Compression okay and even? The other ignition issues for these bikes are the spark units, mounted back by the battery. If you are losing one set of coils and the coils test okay, then swap the spark units in back and see if the spark issue changes sides. If so, then you have a bad spark unit. http://www.cmsnl.com/honda-cb750kz-1979-four-canada_model14694/partslist/F15.htm...
None of the ignition system works well, if the battery won't hold a load test and the charging system is malfunctioning. Go to the Electrosports website for their PDF troubleshooting charts and replacement parts which are far cheaper than OEM parts. Always start troubleshooting with a fully charged and load tested battery. With the stock halogen headlights, there is a big draw at idle and a weak battery will drop voltage down to where the ignition system suffers.
Bill Silver
