You are here:

Motorcycle Repair/1965 c100 no spark

Advertisement


Question
QUESTION: Hi bill,  i was given a 1965 c100.  bike is complete but has not run in 25 years.  checking it out i have no spark.  i purchased a new battery, and looked at diagrams.  i have 1 single black or brown wire going to the coil, and the secondary wire going to the spark plug. the diagram shows a green/white also going to the coil. which is correct.\?  i have cleaned the points, and it appears they are opening at the "f" mark. ohmed out some wire to ignition switch and all seems good.  my son just informed me he "may have" hooked the battery up backwards initially....would that take out the seleniun rectifier?   thanks for any help....Curt Baker

ANSWER: Curt, the C100 has a self-powered magneto ignition, which is not dependent upon a battery. The ignition coil has a black lead (charges the windings) and a green lead which opens/closes the circuit. If you have an erratic spark, it can often be the condenser going bad. Usually no spark is due to dirt/corrosion/wear on the point faces. If you "clean them" with a file or business card, sometimes leftover metal filings or paper fibers can keep the points from closing to make their connection.

It might be wise to remove the flywheel and take a closer look inside for signs of a grounded ignition coil lead or any other damage/wear on the components. Be sure to use the correct flywheel pulling tool for removal. It is a pretty simple system, though. Remember that the ignition switch puts ground on the ignition circuit when you turn the switch to OFF. Try disconnecting the ignition switch at the plug-in connector to see if it is an issue.

Reverse power hookups to the battery/charging system are not a good thing. You can test the rectifier with an ohm meter to see if it was damaged. After 49 years, it might be time to replace it anyway.

Make sure all the light bulbs are good in the lighting circuit as they help balance the charging system along with a fully charged/load tested battery.

Bill Silver

---------- FOLLOW-UP ----------

QUESTION: Bill,  thanks for the advice.  I checked the rectifier   248 ohms in one direction, and OL in the other.  Im guessing thats ok?  i dont have the green/white wire, and have been told it is a late 1965 build,  i only have a black or brown wire to the primary side of the coil, and the heavy secondary to the spark plug.  I have no spark at all, and now possibly bigger problem since the reverse polarity battery incident.  hoping to find a flywheel puller and go from there.   thank you again.  Curt Baker

Answer
Sorry, your reply got buried in a landslide of email recently.

http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php#class  see Z50A diagram for a single wire coil setup. These are AC coils, which function differently than normal DC coils on battery powered bikes. Looking at various eBay listings, I see one and two wire coils available, but the wiring diagrams only show 2 wire.

http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php#class  see C100.

http://www.ebay.com/itm/Honda-Cub-C100-C102-C105-Magneto-Puller-GENUINE-HONDA-07
933-0010000-/151428246663
for an example of the rotor tool Factory ones are more expensive than the aftermarket versions.

http://www.ebay.com/itm/M24-M27-New-Motorcycle-Flywheel-Puller-For-HONDA-KAWASAK
I-SUZUKI-YAMAHA-PEUGEOT-/181540135594 for an example of the Chinese versions.

The reversed battery incident really shouldn't affect the ignition system.

Bill Silver

Motorcycle Repair

All Answers


Answers by Expert:


Ask Experts

Volunteer


Bill 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.

Education/Credentials
3 years auto shop in high school, teacher's aide in Automotive Technology in Jr. College, Diesel mechanic course in college, self-taught mechanic and automotive writer.

©2016 About.com. All rights reserved.