No spark on 125cc tao tao
 

I bought a 125cc tao tao last week and it had some pretty sketchy looking wiring with speaker wire and bare wire showing everywhere. I ordered pretty much brand new everything for it. New wiring harness with stater, new starter, new carb and new brakes. I was hoping I would be able to just plug everything in and it'd work but here I am. I've followed a lot of threads but can't find one that works for me.

1) Unplug the CDI. In the wiring connector measure the resistance of the AC Ignition Power pin to the Ground pin. You should see 400 ohms or so. What do you measure? ~401 ohms

2) Measure the resistance of the Timing/trigger pin to the ground pin. You should measure 150 ohms or so. What do you measure? ~150 ohms

3) Leave the CDI unplugged. Set your meter to measure AC volts on the 100 volt scale. Measure the voltage on the AC Ignition Power pin to the ground pin while cranking the engine. You should see 40 to 80 volts AC while the engine is cranking. What do you measure? Right at around 60v

4) Set your meter to measure AC volts on the lowest scale you have. Ideally this would be 2 volts but many meters don't go down this low. In that case use the lowest scale you have. Measure the voltage on the Timing Trigger pin to the Ground pin while cranking the engine. You should 0.2 t0 0.4 volts AC. What do you measure? Right at 0.2 to 0.4

Now for measuring the output side of the CDI:

A) Leave the CDI unplugged. In the CDI wiring connector measure the resistance of the Ignition Coil pin to the ground pin. You should measure less than 1 ohm (but not zero ohms). What do you measure? 0.5 ohms.

B) Plug the CDI back in. Set your meter to measure AC volts on the 20 volt scale. Set all kill switches to the run position. Crank the engine while measuring the voltage on the Igntition Coil pin to ground. Poke through the insulation of the wire if you can't probe the connector.0! Nothing.

I'm not sure what else to try, any help would be great.

Right, everything to the CDI tests out as right but output from CDI, nothing, so bad CDI though I would expect a lot more volts than 20 so set it to 110v or 250v. However, check the earth to CDI (green) a good earth is vital. Check the kill wire really is open circuit in run with ignition on, and earthed when in kill position. When you fit a new loom you have to be sure all the new stuff and old stuff are connected correctly and compatible, if they are, then you have a dud CDI.

Everything checks out, I swapped a different cdi and still no spark. I actually bought 2 harnesses because I thought the first one was faulty, so I have a spare of everything. Should I maybe try getting a actual ngk spark plug rather than the cheap knockoff that comes with the harness?

Update! I just went out to test everything again and now I'm not getting any reading on the ignition power pin.

Try the old stator, if it has the same wiring as the new one, try the original plug. The old parts are not guaranteed to be right but worth a try, particularly if the old stator tests out OK.

Sorry I've been busy with work, I opened up the cover for the stator and noticed the wires had been rubbed down to bare, so I threw in the old new one and still have no spark, I did test the switch on the handlebar and it's good. Not sure what else to try

Why had the wires "been rubbed down to bare" and did the old stator test out as good when you tried it?

Okay I actually have a proper day off thanks to thanksgiving. So I came out and uncovered the whole harness. Got rid of all the plugs for headlights and such just in case something was messed up there. I retested all the pins to the cdi and here's what I found, everything is good except the resistance from the ignition coil pin to the ground pin, this is fluxuating between 0 and sometimes 0.05 or 0.06 every couple of seconds it'll jump above 1 for a split second. I've checked all the grounds and they look good. Also when I crank the engine measure ac volts from the ac ignition pin to ground I'm only getting like 9 volts and it'll jump into the negatives as well. I might need to charge my battery though but hopefully this info helps

Personally all I test for on the ignition coil wires is voltage, once the CDI is plugged in, you should be getting a high voltage between the wire from CDI to coil, and earth, when the engine is spun. Is this where you are getting the 9v? This seems low, on Hondas it is often 50v to 150v.