CDI Troubleshooting

Courtesy of Ron Marle

The CDI ignition takes a pulsed current generated by the low or high speed charge coil (depending on engine RPM) and charges a capacitor. This stored charge is then discharged into the primary winding of the ignition coil causing the plugs to spark (both at once). The timing of this discharge to the coil is triggered by the arrival of a small electrical pulse generated by the pickup coil and electronically delayed to occur at the proper time by circuits internal to the CDI module. The ignition, engine run and sidestand control unit provide a circuit to ground to "kill" the ignition. There is an old saying "garbage in equals garbage out" If any of these signals are missing or a short circuit to ground occurs in the "kill" circuit, the CDI will be unable to function properly.

Engine Mechanical

Suspected ignition problems are sometimes not that at all but other engine mechanical failures so before we test electricals lets first check the following items :
1. Engine has good compression and the difference between cylinders is small upper 90's for PSI is good for a cold engine.(5 kicks with throttle wide open)
2. Carbs are mechanically balanced. I do this adjustment on the bike using 1/16" music wire as a feeler guage. I adjust the idle stop screw on the left carb untill slight resistance is felt when I slide the wire in and out of the carb mouth under the slide. I then adjust the right carb to match the resistance felt on the left using the balance screw. Then I reset the idle stop screw.
3. Check auto lube pump adjustment
4. Install a set of NEW plugs. The secondary winding of the ignition coil is attached to both plugs. In order to complete the circuit the current must flow down one plug wire to the plug, jump the gap, go thru the engine head to the other plug jump that gap then go back up the wire to the coil. If you interrupt this circuit, neither plug will fire.

Engine Electrical

The RZ electrical connectors can corrode pretty bad the engine vibration helps to maintain good contact but a bike that has set for a while can develope electrical "ghosts" quite easilly. so lets start by seperating, inspecting and re connecting all the electrical connections associated with the ignition system. When that is completed take the following readings. The following readings can be taken using the standard test leads that come with most digital volt ohm meters. The RZ electrical system is connected together with molded nylon "molex" or "spaid" connectors. All the initial readings are taken with the circuit under their normal electrical load. This means that all the connectors are connected and you take the reading by sliding the test probe tip into the molded connector alongside the proper colored wire untill it makes contact with the metal portion of the electrical connector.
1. On the CDI bundle find the connector with the black wire with a white stripe running along it. put the red test lead in along side this wire. hold the black lead against the bare metal of a head bolt. set the meter to read resistance. With the kickstand up, engine in neutral, the kill switch set to run and the ignition key to on you should see greater than 30K OHMS of resistance. if you turn off the key or kill switch the resistance should decrease to near 0. ALL OF THE FOLLOWING READINGS ARE TAKEN DURING 5 RAPID KICKS! The object is to keep the engine rotating long enough for the digital meter to sample the signal and display a reading. This is easiest with the spark plugs removed, The plug wires connected to the plugs and the metal plug bodys connected to each other(I use tape to hold 2 plugs together) to complete the circuit.
2. On the end of the CDI wiring harness you will find a 3 wire connector that has a brown, red and green wire. slide your black probe in beside the brown wire and the red probe in beside the green wire. this is your low speed winding. set the meter to read AC volts, turn on the ignition and kick the machine over 5 times quickly. you should see, while kicking, a reading of 25 Volts AC.
3. Now move the red test lead to the red wire (measuring brown to red) this is the high speed winding kick over the machine with the ignition on and you should see 4.5 Volts AC.
4. On the CDI bundle there is a 2 wire connector with a white with red stripe wire and a white with green stripe wire. This is your pickup coil connector. Slide your test leads in beside these 2 wires. When you kick the starter rapidly you should see 0.3 Volts AC
5. On the CDI bundle there is a 2 wire connector with a orange wire and a black wire. Slide the meter probes in beside these wires. This is the CDI output to the ignition coil primary winding. When the starter is kicked rapidly, you should see 0.4 Volts AC.
If any of these voltages are missing one of 2 things is happening. Either the source device is not generating the signal or the destination device is shorted and the signal is being loaded down. If one of the signals is missing, seperate the electrical connector for that signal(electrically unload it) and connect your meter to the source side and repeat the test. Here are the unloaded readings for the above listed signals :
2. Low speed charge coil 50 Volts AC unloaded
3. High speed charge coil 4.5 Volts AC unloaded
4. Pickup coil 0.3 Volts AC unloaded
5. CDI output 24 Volts AC unloaded
In the case of signals 2,3 and 4 if the loaded test is bad and the unloaded test is good do a resistance test of the source device. The low speed coil (test 2) should read 225 ohms (or 133 ohms depending on engine type). The high speed coil (test 3) should read 5.3 ohms and the pickup coil (test 4) should read 115 ohms. If the resistance check is good the CDI is most likley at fault.
In case the signal 5 load test is bad and the unloaded test is good, measure the resistance of the ignition coil primary winding. The primary winding resistance is around 0.33 ohms. If it is OK then the CDI is most likley at fault. If all the above readings are good then check the secondary winding of the ignition coil, the measurment from one plug cap to the other should be about 23K ohms. The plug caps themselvs "screw" (twist counterclockwise)off of the plug wires each plug cap should read about 10K ohm when measured by themselvs. The coil and plug wires alone should read 3.5K ohms. It is possible for the coil secondary to be breaking down under high voltage but measure just fine with the ohm meter. If you are getting the proper signal on the black and orange wire to the coil with no spark out into NEW plugs, then the coil is probably at fault. I had this happen intermittently for about a year, I finally found it by connecting up a meter to the black and orange wires and taping it to the tank where I could see it. The next time the bike quit, while I was coasting in gear the input voltage was still there with no spark out, Good in, garbage out. told me it was the coil. One final word of caution.