1986 TRX125 ignition issue
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Although it is possible it is the CDI at fault, the usual culprits for this type of fault are coil, or stator, or trigger coil. Can also be fuel related, tank vent blocked, or running rich, etc. If you can, check for a spark when the fault is on. Change the plug too, it could be as simple as that. If you do need a new CDI, a modern Chinese 125 CDI could be made to work, but it takes an expert at CDI electrics to do it.