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Motorcycle Repair/1981 MT 70 honda trail bike

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Question
You gotta love the older bikes.  I am working on my Boss's trail bike that he just picked up.  It was sent to a repair shop 2 yrs ago and never touched .  I was wondering how to check the primary coil on this gem.  My externalchecks out ok according to the manuals specs for it.  I pulled the stator windins of the plate behind the flywheel measured them and this is what i have for resistance. light coil measured at 1.2 ohms from white wire to ground terminal after windings and the second wire which was yellow measured only .7 ohms to ground lug.  No direct shorts so far.  The primary coil which is my spark coil measured 2.5 ohms from leed wire to ground lug.  Points look good although i cant check the capactor.  This bike had set for years before my boss got it.  Any guidence would be great thanks in advance for any help.  Joe

Answer
Joe, I'll assume that the model is a CT70, not MT70.

If you had a low voltage signal coming out on the black wire, feeding the primary windings on the coil, then the primary magneto coil is probably fine. You really have to disconnect each coil from anything else to ensure accurate readings.

Condensers do fail with age and mileage, but it isn't all that common. Usually all that happens with these bikes when they have sat for years is that the point contacts get corroded and don't make a clean contact connection. If the points are deeply pitted, that is an indicator of a weak condenser, however. Failing condensers will show erratic spark to the spark plug. Use a non-resistor spark plug and cap for best results. If in doubt, just buy another new condenser and install it, as long as you have the plate all apart.

If the ignition switch is suspect, just unplug it to remove the ground to the ignition system. The ignition switch puts ground to the ignition in the OFF position, as does the KILL switch.

Bill Silver  

Motorcycle Repair

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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.

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