1979 QT50 Ignition Issue - HELP

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1979 QT50 Ignition Issue - HELP

Postby Kurt » Fri Jun 21, 2013 6:31 am

I have a 1979 QT50 puzzle that I can't seem to solve. The moped was running when I bought it but the previous owner hinted of an ignition issue. "Runs well for awhile but will not restart unless it sits". This quickly moved from an intermitent problem to a no spark problem. The previous owner had replaced the coil. I worked through the wiring and didn't find any issues and the ground is good. I replaced the CDI and it started and ran well for about 2 hrs. At that point the issue started all over again, weak to intermittent spark and then no spark at all. Changed the spark plug too. Along with any guidance on the issue I have the basic question. Should there be some resistance across the terminals of the CDI if it's good, or bad?
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re: 1979 QT50 Ignition Issue - HELP

Postby John » Fri Jun 21, 2013 7:07 am

Does it have a battery, if so replace. Condenser at the stater maybe.
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re: 1979 QT50 Ignition Issue - HELP

Postby Kurt » Fri Jun 21, 2013 9:38 am

Thanks for the reply. The battery is brand new and fully charged. Regarding the condenser, does it have one if it has a CDI? I'm seeing the ignition coil, the lighting coil and the pulse coil. I have the electrical schematic from the shop manual and ~95% of it matches. It doesn't have the engine control module or circuit on the speedometer/key on-off. Not sure it this extra info helps or not.
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re: 1979 QT50 Ignition Issue - HELP

Postby Kurt » Fri Jun 21, 2013 11:54 am

Looking at the schematic and the actual wiring it doesn't look like the battery is part of the ignition system. Can a bad ignition coil cause a CDI to stop functioning? Can anyone tell me now to determine if a CDI or ignition coil are good or bad......I hate electrical issues.
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Re: 1979 QT50 Ignition Issue - HELP

Postby Arlie1180 » Sat Jan 31, 2015 10:29 am

Charge coil is bad. Yamaha had faulty ones that year and changed them in 80-81. CDI rarely go bad. PW50 has the same charge coil.
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