Hello,
I have a situation with a 110cc quad that belongs to my nephew. It was bought last year and worked great all summer. It then sat over the winter, and wouldn't start this spring. There seems to be an issue with the spark. It is very weak, and intermittent. There are times when there will be no spark while cranking, and then a couple weak sparks, and then even possibly a good strong spark.

There have been two times while trying to troubleshoot that it started for a second, and then die off.

I bought a new CDI after reading all of the problems that people have had. My brother in law also bought a CDI at one time and said it ran for about 5 minutes and then died and wouldn't start again.

I'm thinking the issue isn't with the CDI, because the weak/intermittent spark seems similar with both CDI's installed.

What can I check as far as the coil and the magneto to try to troubleshoot?

 

Disconnect the CDI and measure the AC ignition power voltage while cranking the engine. Set you meter to AC volts on the 200 volts AC scale. What do you measure? 45 - 80 volts AC is what you should be seeing.

Measure the timing trigger voltage pin next. Set the meter to the lowest AC voltage scale you have. What do you measure? 0.2 to 0.4 volts is ballpark.

Reconnect the CDI and measure the AC voltage to the ignition coil while cranking. Do you see any voltage spikes? How high do they go? Try both CDIs. Do you see any difference between them?

 

Thanks for the advice. Here are my measurements...

AC Ignition Power - 0.1 when cranking, 3.5 volt spike when I stop cranking
Timing Trigger Voltage - 0.2 to 0.4 when cranking, 0.8 spike when I stop cranking

After connecting the CDI.....
AC voltage to coil - only saw spikes when I stopped cranking. The largest spike was 6.8 volts.

I then measured the AC voltage of the various wires coming from the magneto (in case that tells you more).
I disconnected the harness, and used the green ground wire from the magneto as ground.
Blue/White wire - 0.1, maybe 0.2 volts
Black/Brown(Red maybe) - 44 to 45 volts
Yellow - 3.7 to 3.8 volts
White - 4.8 to 5.0 volts

After taking the magneto cover off it looks like the blue/white wire runs to the timing trigger I'm guessing? What should the gap on this be? How is this gap measured with the cover on?

Thanks again for your help. I'm not sure how I would troubleshoot this without your advice!!

 

The AC ignition power wire at the CDI (0.1 volts AC cranking) should be the same wire as the the Black/Brown (maybe black/red) where you measured 44 to 45 volts AC.

This is wrong. Double check those measurements. If the measurements are true then you have an open wire from the stator (black/red) to the CDI AC ignition power pin (also black/red). Look carefully at the stator connections to the wiring harness.

 

That makes perfect sense. The measurements are true, as I measured everything several times with the same results.

I'll start pulling the wiring harness apart tonight to chase that wire and see if it's open anywhere.

Thanks again for your help. Have you thought about writing a repair manual/book on these things? You are quite knowledgeable!

 

Ok, I measured the AC Ignition voltage again tonight after not finding any bad wires - and it measured about 45 volts. Not sure what was different from the other night.

I suspect that I may have been confused and measuring the Ignition coil voltage that measured approximately 0.2 volts, and spiked to 3.5 to 6.8 volts when I stopped cranking. Does that seem right?

I'm really not sure where to go from here. Any extra help would be great.

 

When you crank the starter and measure the ignition voltage, do this over 20 seconds. Do you see any voltage spikes during that time?

Or do you only see spikes when the starter is turned off?

 

I measured the AC voltage going into the coil, before the spark plug.

When i start to crank, I get a quick spike - around 1.5 volts AC.

While I'm cranking I see 0.8 - 0.9 volts AC. This is very constant - no spikes.

When I stop cranking, I see a spike - anywhere from 5.0 to 8.5 volts AC. This varies every time.

 

Measuring the voltage at the coil with a meter is fraught with difficulties. The voltage here is supposed to be very high and very narrow spikes ringing back and forth at about 30,000 times per second. Regular meters aren't designed to measure this type of waveform, and so one meter may not read the same as another. On the other hand, meters are what we have so we take in as much data as possible and make the best conclusions from that data - even if it is less than optimum.

What most meters show at the coil drive pin from the CDI is mostly very low voltages with random much higher voltage spikes in between. These spike are when the meter happens to sample the voltage right when the CDI is firing.

It appears that you do see a spike when the starter is turned off, but see no spikes when the starter is turning. The 'no spikes' when the starter is turning suggests strongly that the CDI is not getting triggered. The spike that occurs when the starter turns off sugests that the CDI *can* be triggered. Starters draw a lot of current, and when they are abruptly shut off the inductive kickback can produce transient spikes that could trigger the CDI.

Question: When you get that voltage spike upon turning off the starter
motor do you also get a spark? That would give more credence to the theory that the CDI is getting fired when the starter is turned off.

Your trigger voltage is on the low side. But once again this is a complicated fast moving +/- spike waveform that isn't measured well by voltmeters either. No trigger and low trigger voltage points to the stator timing/trigger signal.

The output voltage from the timing trigger pickup coil is affected by the gap between the pickup coil and a raised bump on the outside of the flywheel that passes under the pickup coil. Narrower gap = more trigger voltage. Most quads are not adjustable, but some are. Eton quads specifiy this gap at 0.025".

Also, if steel debris (chips, rust particles, etc) get lodged in the pickup coil that will reduce the timing/trigger output voltage also. The pickup coil has an embedded magnet in it that senses (in conjunction with the pickup coil) the steel raised bump that passes by. That magnet attracts magnetic debris and as it accumulates on/in the pickup coil it shields it the effect from the raised bump on the flywheel as it passes by - lowering the trigger voltage. You may want to see if the trigger coil is clear of steel bits stuck to it.

 

I have learned many lessons in my life the hard way.

1) When changing oil, always replace the drain plug before refilling the engine oil.
2) When boating, remember to put the plug in before backing down the ramp and into the water.
....ETC.

I now have a new "learned lesson".

When working on electrical issues always ALWAYS check the main connections to the battery.

I ripped apart the entire wiring harness tonight to find whatever bad wire MUST be causing my problem. I made it all the way to the battery with nothing found. Coming off the positive side of the battery was one wire, that went into a wire nut and split into two large red wires - one wire went into a fuse. That fused red wire was corroded and had a minimal connection.

I fixed that, and bam, bright blue spark. Short time later, with carb adjusted, the engine fires and runs like a top.

Thank you for all of your help. It was much appreciated!!