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We have a Chinese motor cycle 125cc off road, last time used…

Customer Question
Hi we have a...

Hi we have a Chinese motor cycle 125cc off road, last time used 3 months ago started and ran good. tried to start today, no spark tried new spark plug , no spark. in pluged ignition cdi, tested voltage out of engine 116volts. checker wiring to switch with ohm meter circuit good, switch worked ok on off. ignition coil 11 ohms primary, secondary was 4 ohms, spark plug cap 1,4 ohms. does any thing look incorrect, is there away to check ignition cdi . volts to the ignition coil from cdi ,what would I expect to measure . thanks Jeff

Mechanic's Assistant: Have you checked all the fuses? Do you have a wiring diagram?

No fuses no wiring diagram cheep 2nd hand Chinese moto bike

Mechanic's Assistant: What is the model/year of your motorcycle?

In fortunately these bikes dont have model or year plates on them. wiring is , 2 wires magneto to cdi, 2 wires cdi to on off switch, 2 wires to ignition coil, lead to spark plug

Mechanic's Assistant: What year is your motorcycle?

3 wires from magneto to cdi

Mechanic's Assistant: Are you fixing your bike yourself? What have you tried so far?

Yes, no spark at plug. can you read first page , description of what I have tried and measured.

Mechanic's Assistant: Anything else you want the mechanic to know before I connect you?

Not at this point

Submitted: 10 months ago.Category: Motorcycle
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Answered in 17 minutes by:
9/28/2017
Motorcycle Mechanic: Louie, Technician replied 10 months ago
Louie
Louie, Technician
Category: Motorcycle
Satisfied Customers: 13,499
Experience: 25+ yrs. experience
Verified

Hi and welcome to JustAnswer, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.
Initially, please measure again the resistance of the ignition coil's primary and secondary.

This is an independent site and members of this online community provide information, repair tips, technical assistance as a form of paid Q & A service.

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Customer reply replied 10 months ago
have quality meter now primary .4 ohm secondary 4390 ohms
Motorcycle Mechanic: Louie, Technician replied 10 months ago

Appreciate the post back of new readings.

And the "...voltage out of engine..."? ...pulsating when attempting to start?

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Customer reply replied 10 months ago
wires in pluged from motor magneto 3 wires kicking over motor blue/white to green 55v, black/red to green 0v, blue/white to black/red 75v . if I could kick it harder I think I would get more volts, kicking motor over voltage rises and fall with motor rotation and kicking
Customer reply replied 10 months ago
spark plug cap has 1.5 ohms resistance, is that ok
Motorcycle Mechanic: Louie, Technician replied 10 months ago

This is significant. It would appear that 'magneto' has two (2) coils; pickup/pulser coil and exciter coil (capacitor charging).

Please measure the resistances of pairing the 3 wires:

  • blue/white to green - ___Ω;
  • black/red to green - ___Ω;
  • blue/white to black/red - ___Ω.

For the spark plug cap, the lower the better.

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Customer reply replied 10 months ago
red/black to blue/white 510.9 ohms, black/red to green 379.5 ohms, blue/white to green 132.6 ohms
Motorcycle Mechanic: Louie, Technician replied 10 months ago

Based on these readings, it would appear that the green wire is the common ground.

Please measure again the voltage between the black/red to green when attempting to start.

We are to expect very low pulsating voltage.

And is there any Ω reading from this green wire to engine ground?

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Customer reply replied 10 months ago
green to earth/engine .5 ohm, kicking over motor, measureing green to red/black, kick 1 o volts, kick2 50/60 volts, kick3 o volts,kick4 o volts,kick5 50/60 volts looks like loose bad connection recording different reading as kicking each time
Motorcycle Mechanic: Louie, Technician replied 10 months ago

The readings:

  • blue/white to green 55v = is good;
  • green to earth/engine .5 ohm;
  • 0.0Ω would be better;
  • green to red/black, kick 1 o volts = bad;
  • kick2 50/60 volts = bad.

Either way then 1 of the coils in the magneto is bad or intermittent.

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Customer reply replied 10 months ago
ok thank Louie will take off magneto cover off tomorrow to see what I can find. Jeff
Motorcycle Mechanic: Louie, Technician replied 10 months ago

Yes please; an update then when able.

And clear pictures of the coils. Click HERE.

These pictures would then serve as common references.

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Customer reply replied 10 months ago
hi Louie , removed magneto, black/red wire open circuit, replaced wire. now have 70 volts . this is from coil in magneto, other side of coil to frame. blue/white wire goes to sensor beside magneto , small raised dot on out side of magneto rotates past sensor (position sensor / spark plug firing). With every thing connected , no spark ,cannot get voltage reading to earth on blue/white wire to earth. ohm meter blue/white to earth 132.2ohms, kick over bike resistance fluctuates between 0 to 200 ohms as motor /magneto rotates, does mean sensor ok.? kill switch at cdi , switch off, circuit with ohm meter. switch run no circuit, connect cables measure 60 volts going to switch . wire starts at cdi up to off run switch back to cdi, I assume switch ok. at this point I'm thinking cdi may have failed, assuming position sensor ok. any ideas Louie , thanks Jeff
Motorcycle Mechanic: Louie, Technician replied 10 months ago

Hi again Jeff;

The 70V on the black/red would be the excitation/capacitor charging to the CDI = good.

The blue/white should produce pulsating low voltage; i.e. ~ 500mV when attempting to start.

Try (temporarily) disconnecting all other wires to/from the CDI except:

  • black/red;
  • blue/white;
  • green (or ground);
  • and the 2 wires top the ignition coil (presumably 1 wire is ground too).

If possible, post back clear pictures of the ignition coil and CDI+wires and the magneto/sensor+wires.

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