CDI and magneto test

Longshot270

Longshot270

New Member
I'm having trouble with my bike where it wont start. I can pedal up to about 15 mph and drop the clutch and it will only engine brake. It will occasionally fire but only once or twice. Sometimes it'll run for a few seconds. I'm calling it an electric issue because fuel and air are good and when I pull the plug I don't get spark besides one or two occasional flashes. After doing some reading I got out my old wavetek HD110.

Here are my results

CDI test
Wire-------------Expected----------Observed
Black to Blue------1150K-------------Infinite
Black to plug------2.6 K--------------7.39 K
Blue to Plug-------1150K-------------Infinite

Magneto test
Wire------------Expected------Observed
Blu to Wt--------327-----------364
Blk to Blu--------327-----------Infinite
Blk to Wt--------2.1-----------Infinite
Blk to Gnd-------0-------------0
Blu to Gnd-------327-----------Infinite
Wt to GND-------2.1-----------Infinite

I'm guessing this means both my CDI and magneto are either burnt or have bad connections? I'm leaning towards bad connections since I have a single spark occasionally. I didn't try pushing the probes through the insulation so I'll give that a try and see if anything changes but I figured it'd be good to post what I know at this point in case anyone has seen this trend before.

Thanks in advance
 
Hello,

You need to set your ohm meter to 20k for both tests.
Magneto
Blue to White 0.25-0.40
White to Black 0.0
Blue to black 0.31
CDI
Spark plug boot to black 2.0-2.7
Spark plug boot to blue no change
Blue wire to black wire no change

I have found the clutch needs adjusting to properly fire. It maybe slipping once engaged.

Good Luck
 
Budz said:
Hello,

You need to set your ohm meter to 20k for both tests.
Magneto
Blue to White 0.25-0.40 .37
White to Black 0.0 1.
Blue to black 0.31 1.
CDI
Spark plug boot to black 2.0-2.7 7.44
Spark plug boot to blue no change 1.
Blue wire to black wire no change 1.

I have found the clutch needs adjusting to properly fire. It maybe slipping once engaged.

Good Luck
Click to expand...
Results in blue

Clutch has been good. I was able to do burnouts before and turns the engine normally while moving with no spark.
 
Longshot270, after looking at your readings it seems the black wire is the problem. The full magneto coil reading looks fine. Since you said that occasionally it fires then I would check the black to mag armature for an intermittant connection. Take the magneto out of the engine to inspect it very closely. Good luck and tell us what you found.
 
I think it is a connection on the magneto that is causing it. While inspecting it yesterday the wire that connects the coil to the blue wire snapped off. Now I've got to either find a way to reconnect it or buy a new one.
 
how many volts does the blue wire coming off the cdi produce? not the blue wire from the engine, the blue wire from the black box. and does the cdi have a voltage regulator in it?
 
bigbutterbean said:
how many volts does the blue wire coming off the cdi produce? not the blue wire from the engine, the blue wire from the black box. and does the cdi have a voltage regulator in it?
Click to expand...

Isn't that the wire that feeds the CDI? When disconnected it would be 0.
I do not know if it has a regulator. It was the one that came in the kit. Because I couldn't get any similar readings I replaced both the magneto and CDI.

The new combo runs, but not as smooth as the previous one.
 
yes, i realize that disconnected it would be zero. both my cdi wires have dual connectors, and i have an idea i may share later on. for now, i just want to know what the blue wire coming off the black box produces when connected. sine its a wire coming off the cdi, not sure how it would feed the cdi. when you connect a cdi, you connect blue wire from cdi to blue wire from mag, and black wire from cdi to black wire from mag. im asking about the blue wire from the cdi, when connected to the mag and all other wires are connected correctly. should it produce 6v? i would also think that the black box would have a regulator built in so it didnt blow up, but i need to know from someone who knows for sure.
 
It wouldn't produce voltage, the magneto produces voltage. The cdi is fed the voltage through the blue/black wires and feeds out ~20,000 volts to the spark plug through the thick black wire. and the magneto voltage varies depending on speed, 10-100 volts in my experience, in a 49cc motor.
 
Longshot270 said:
I'm having trouble with my bike where it wont start. I can pedal up to about 15 mph and drop the clutch and it will only engine brake. It will occasionally fire but only once or twice. Sometimes it'll run for a few seconds. I'm calling it an electric issue because fuel and air are good and when I pull the plug I don't get spark besides one or two occasional flashes. After doing some reading I got out my old wavetek HD110.

Here are my results

CDI test
Wire-------------Expected----------Observed
Black to Blue------1150K-------------Infinite
Black to plug------2.6 K--------------7.39 K
Blue to Plug-------1150K-------------Infinite

Magneto test
Wire------------Expected------Observed
Blu to Wt--------327-----------364
Blk to Blu--------327-----------Infinite
Blk to Wt--------2.1-----------Infinite
Blk to Gnd-------0-------------0
Blu to Gnd-------327-----------Infinite
Wt to GND-------2.1-----------Infinite

I'm guessing this means both my CDI and magneto are either burnt or have bad connections? I'm leaning towards bad connections since I have a single spark occasionally. I didn't try pushing the probes through the insulation so I'll give that a try and see if anything changes but I figured it'd be good to post what I know at this point in case anyone has seen this trend before.

Thanks in advance
Click to expand...

I'd say all you've got wrong is an open magneto coil.

All of mine have about 350 ohm between the black and blue wires.

I don't believe you can check the CDI other than substitution.

What I do is check the mag coil first, because it's easy to check. If its bad, replace it. If it's good, replace the CDI.
 
adding to the above post, I had a magneto break at the solder connection where the ground wire is attached to the metal plates. this caused an infinite reading between black and blue/white wires. 5 minutes of soldering and it was fixed.
 
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