AboutBill Silver Expertise Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.
Experience I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.
Organizations VJMC (Vintage Japanese Motorcycle Club) of North America
Publications VJMC newsletter, as editor for two years and as contributing editor currently.
Expert: Bill Silver Date: 7/8/2008 Subject: Honda Cb125s has no Spark
Question Hello Bill,
I recently purchased a 1978 Honda Cb125s. The bike has no spark, and I have been racking my brain trying to figure out why. I have replaced the spark plug, ignition coil, points, and the condenser, and all the wiring seems to be fine.
The ignition switch and kill switch are on.
one thing that i don't fully understand is that in the repair manual it states that to check the ignition timing you should hook up a 12v-3w lamp across the line, then when the lamp goes out you can adjust based on the F mark. The lamp never lights up at all when I connect the lamp, could this be a clue?
I really would appreciate any help you can give. Based off of other answers you have given on this site, you seem to really know your stuff.
Thanks!
Answer Abhimanyu, First thing to know is that these bike's ignition systems are battery-powered... 6volts. If you are thinking that it is a self-energizing magneto, you will waste more time and money. It needs a fresh and fully charged battery to run properly.
Go to: http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php find your model and trace the wiring colors. Use the 1976 diagram, which should be close. Remember to check all the GROUND connections as well as the ones with volts/current flow.
Use a low-powered test light (6v) or volt meter to follow the flow from the battery, to the ignition switch, up through the kill switch and back down to the + side of the ignition coil. The points are just a timed switch to turn the coil magnetism ON and OFF at the right time.
The points MUST BE
CLEAN... nothing but shiny metal across the two contact surfaces.
GAPPED.. .014" (.04mm?) when the points are at the highest part of the point cam.
TIMED... so that they just OPEN when the F mark aligns with the pointer on the stator windings. The test light/meter will not show any voltage until the points OPEN. The condenser just helps to suppress the arcing across the point contact faces, when they are opening and closing, due to the current draw across the contacts.
