This article deals with Piaggio ignition fault finding where the scooter has no spark and covers Piaggio Zip 4-stroke 50cc and 100cc

Testing for a spark

We've already covered testing for a spark in our previous article Piaggio Ignition Fault Finding which dealt with 2-stroke Piaggio Moped ignition, so we won't cover it again but suffice to say it isn't enough to look at the sparkplug to see if there is a satisfactory spark or not. In the workshop we use a simple spark tester or you can make your own as described in the linked article.

As described in the previous article you need to see a spark of at least 6mm otherwise there is an ignition problem.

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The ignition components and wiring is the same on the 4-stroke 100cc zip as the 4-stroke 50cc zip and is almost completely independent to the rest of the scooter wiring/ electrical system. This means that the ignition can continue to function and the engine continue to run regardless of any faults that occur in the lighting/ battery/ other electrical functions of the bike.

Once you've established there is no spark or an inadequate start it's fairly simply to start narrowing things down, in the previous article we explained the basics for using a multimeter so we'll skip straight to the testing.

Testing the flywheel pickup
The flywheel pickup sends a pulse to the cdi everytime the flywheel completes a full rotation and from this the cdi can calculate the speed the engine is spinning (rpm) and the exact position of the crankshaft (and therefore the piston) so as it can make an informed decision of when to make the spark plug spark.

To test it unplug the connector block from the cdi which is found behind the panel which sits behind the rider's heels (close to the spark plug). There should be a reading of between 120 ohms and 180 ohms between the brown pickup wire and earth point (e.g. the - terminal on the battery)- you may need to push a pin into the connector block to access the pins.
If you get this reading the pickup and pickup wiring are almost certainly ok, it's very rare for there to be a problem if you get this reading.
If you don't get this reading unplug the 2 wire connector coming from the stator and test the wire coming directly from the stator/ pickup assembly (by the fan cover) which was connected to the brown wire- if you still don't get the correct reading directly from here then the pickup is faulty and will need replacing.
If you are getting the correct reading at the cdi then remove the fan cover. As you turn the flywheel with your hand you'll see it has a 'nobble' which passes the pickup every rotation, the gap between this nobble and the nobble on the pickup should be no more than 1mm, any more than this and the pickup may not be triggered.

Testing the killswitch wire
When you turn the ignition key off this connects the green wire to earth and tells the cdi to stop sparking. If you cut or disconnect this wire you won't be able to turn the moped off with the key, so to test this all you have to do is check for continuity between earth (e.g. negative at the battery) and the green wire at the cdi connector (with the block disconnected)- there should be no continuity whatsoever (test on a high range e.g. 10 million ohms) when the key is in the 'on' position and there should be 0 ohms (full continuity) between this wire and earth when the key is in the off position. Check carefully, if the ignition switch is faulty it can have a 'medium' resistance which may allow the bike to start but cause poor running or cutting out if say the switch gets wet. If you're unsure you can temporarily disconnect the green wire from the cdi to eliminate it for testing.

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Testing the earth wire
This one is easy, just disconnect the cdi connector block and check with your multimeter there is continuity between the black wire and earth. You should have a reading of 0 ohms.

Testing the stator coils
The 4-stroke Piaggio Zips are a little unusual. Normally on mopeds there is one stator coil for the ignition which powers the cdi, and completely separate charging coils to power the lights and charge the battery. On the 4-stroke Piaggio Zip scooters there is just one set of coils (the blue/grey wire) which powers the cdi *and* also goes to the regulator to charge the battery and power the lights. This is why there are only 2 wires coming from the stator assembly- one for the pickup coil (brown) and one for the stator coils (blue black). The coils also connect to earth internally through the bolts holding it to the engine.

To test it disconnect the cdi block connector and check the resistance between the blue/grey wire and earth, it should be approx 0.7 ohms. If you then crank the engine with the multimeter set to AC volts (not DC!) you should get a good 8-9volts AC between this wire and earth, this reading should not drop substantially if you test it again with the cdi plugged in.
If you don't get this reading disconnect the regulator connector block temporarily as the blue/ grey wire also goes there and this eliminates the possibility (although unlikely) that the regulator is faulty and shorting out the wire and then repeat the test. The regulator is located under the front fairing panel and can be recognised by its cooling fins.

If all of the above tests check out ok there is no other real option than to replace the cdi module