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Louie, Technician
Category: Motorcycle
Satisfied Customers: 12590
Experience:  25+ yrs. experience
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GN125 (1999 assembled) cuts out completely about every 2

Customer Question

GN125 (1999 Jap assembled) cuts out completely about every 2 seconds under medium to hard acceleration then kicks back to life for another 2 seconds and continues doing that like a bucking bronco. There is no backfiring or spluttering. Have fitted brand new carb, CDI, battery, coil, spark plug and lead. Air filter is clean as a whistle and I fitted another second hand exhaust system. Have tried isolating the kill switch but makes no difference. Have gone through every wire connection I can find inside headlight, under seat and chassis. Couldn't find any corroded terminals. Tank is clean and free of rust. Fuel hose flows freely. I have owned the bike from new and it has only done 16000 original ks. Still on original tyres. It resides on the south pacific tropical island of Rarotonga, Cook Islands.
Submitted: 1 year ago.
Category: Motorcycle
Expert:  Louie replied 1 year ago.

Hi Dennis and welcome to JustAnswer,

Thank you for the question and your patience. Should you still need assistance for information purposes only...

Initially, other than the KILL switch, have you checked/bypassed the ignition switch? ...the ENGINE RUN/OFF switch? (depending on the version)

Still, it would appear to be either a fuel delivery issue (least likely) or an intermittent spark (most likely). Since "...CDI, battery, coil, spark plug and lead..." have all been replaced, then proposed preliminary tries (if have not been done):

  • • verify ground connection of pulser (pickup) coil;
  • • ensure good connection from the pulser coil to the CDI.
Customer: replied 1 year ago.
I assume by pulser coil you mean ignition coil? I connected a multimeter to both wires at each end of coil to CDI, wiggled the loom with no fluctuations.
Next to the starter solenoid and battery there is a small black box with Nippondenso on the top. Is this a condenser and could it be the problem?
Expert:  Louie replied 1 year ago.

Sorry Dennis but no. The pulser or pickup coil is co-located in the stator area. In old school this is the equivalent of a contact point or breaker. It triggers the ignition coil to fire or in this case, the CDI to discharge its capacitor to the ignition coil inducing the spark.

Customer: replied 1 year ago.
That sounds like it could be the problem. Where do I find the stator? What does it look like?
Expert:  Louie replied 1 year ago.

The stator area is at the left crankcase.

Please click HERE. Encircled in red is the pulser/pickup coil. The multiple coils are the stator windings.

Expert:  Louie replied 1 year ago.

Equally suspect would be the charging system. If the battery is getting too high a voltage, the ignition electronics kicks in auto-protect and shuts down the engine momentarily almost like a rev limiter.

This is simpler to test; run the GN125 with the voltage regulator temporarily disconnected and/or measure the battery voltage when revving.