Possible CDI for a Yamaha Champ 100CC, no spark.

[Finnforest]

Hello everyone, this is one of my first posts here 😃 , im having some trouble with the kids bike, no spark. What i measured so far at the CDI is:

 

Shutoff wire works ok

It has ground

It has connection to the ignition coil.

Pickup coil measures 325 ohm

Source coil measures 393 ohm

 

The ignition coil seems fine when i measure it. new sparkplug too. Flywheel spins and the key is in place.

Havent found a service manual for the champ so checked the pickup coil and the source coil values in a yamaha badger manual.

Is the cdi a common problem on these old machines? And where can i get a new cdi? Used ones i can get from ebay, but i have kids in different ages so i got like 10+ more years of use for it 😃

 

[Lawman86]

Yes they are known issues. If you can locate the ohms values +/- a few ohms you should be good to go. If is not the CDI I would check they charging system output. I know on a few atv’s and dirt bikes that won’t run At all without  the charging system running at all times to charge it all. 

[Finnforest]

Had some time to take some more measurments, the source coil is putting out AC 24,7 Volt when i run it on the starter. Hooked up an oscilloscope to the pickup coil and it vas about 1,2Vols up n down. So they "seem" to work atleast there is some life in them. Measured the output from the CDI to the coil and dint get any DC reading but 8V AC. I think the cdi should output DC and waay more than 8V. Turned off the light in the garage and there was actually a tiny tiny spark. My money is on the CDI atm. Please prove me wrong 😃

[Lawman86]

51 minutes ago, Finnforest said:

Had some time to take some more measurments, the source coil is putting out AC 24,7 Volt when i run it on the starter. Hooked up an oscilloscope to the pickup coil and it vas about 1,2Vols up n down. So they "seem" to work atleast there is some life in them. Measured the output from the CDI to the coil and dint get any DC reading but 8V AC. I think the cdi should output DC and waay more than 8V. Turned off the light in the garage and there was actually a tiny tiny spark. My money is on the CDI atm. Please prove me wrong 😃

CDI was my first guess. I’ve measured several over the years with an ohmmeter and the factory specs and it’s usually really quick to rule out. You should be getting a bright blue spark. Also 8 volts to the CDI could mean there’s a small section of the wire that’s pinched, chafed, or just a low battery. 8v is not enough to do anything. I’ve had to reword several bikes and Fourwheeler’s due to corroded wires. That green crust will cause a low reading as well

[Finnforest]

Im getting 24,7V AC into the cdi, its 8V from the output to the ignition coil. No green crust anywhere, took every connection apart.

[Savage3]

You can test the CDI for a short by using dvom to test between gound pin and the other pins. If there is continuity,  the CDI is shorting to ground.

Also, unhook the kill wire and then check for spark before buying new CDI.

[Finnforest]

No shorts, pulled the CDI apart now, almost got all silicone off. I post some pics later 😃 , alteast no diodes where burnt inside, no shorts in the capacitators either. I have to pull the microscope

so see at the markings to id some of the circuits.

[Savage3]

I cant6say for sure without viewing specs, but, the pick up coil resistance appears a little high.

Check the voltage and current on that as well.

Also check the air gap on pick up.

[Freezeman]

Any progress? I have an 80 Moto4 with the same type problem. I bake the CDI in the oven which makes it spark for a while yet it would be nice to find a new one or a real fix for it.

[Savage3]

What is the uf rating on capicitor? What were the results of your test with dvom? Sounds like you missed something when testing capacitor.  8 volts seems low. Remember,  check wire going from cdi to coil. Just because it has continuity, does not mean it can carry full current.

[Finnforest]

Hello again, working slowly on the cdi, got alot of other things to do, like 4 kids 😃 , i used my function generator to simulare the pickup coil and the signal reaches the thyristor just fine, so i belive the fault

is the thysistor itself or perhaps the large cap that discharges to the coil, i have ordered a desolder gun so i can delsoder and measure off circuit.

 

The pickup coil was given out 1,5V and the airgap is very tight.

[Savage3]

1.5 sounds a little high, usually see less then a volt, but, check manual or possibly the meter is off a little.

Use about .010 feeler guage for air gap, a business card will usually work.

Disconnect CDI, test for continuity between ground pin or pins (sometimes two ground pins) and all the other pins. There should be NO continuity. 

The wire from pick up should be going directly to CDI.

Is the CDI a/c or d/c ?

[Savage3]

Also, if you have a kill button, disconnect wire from CDI, then crank and check for spark with wire disconnected.