This comes up an awful lot, so I thought I'd write up a FAQ on it. First of all, some background: All XJ's, and most street Yamahas, use TCI (Transistor Controlled Ignition), not CDI (Capacitive Discharge Ignition). TCI is very much like a "classic", points-based, ignition system, but it uses transistors instead of points to charge and fire the coils. The biggest difference between CDI and TCI is that CDI coils need a couple of hundred Volts to fire them, while TCI coils need 12 Volts. This means that TCI and CDI coils and control modules are very much NOT INTERCHANGABLE. How TCI works (You probably should read this, but you can skip right down to troubleshooting if you want.) The TCI module itself is, more-or-less, two ignition "channels" in one box. One channel, with the left-side coil, handles cylinders 1 and 4. The other channel, with the right-side coil, takes care of cylinders 2 and 3. Since there is very little in common between the two channels, it's relatively rare that a complete lack of spark on all cylinders is caused by a bad coil... they would both have to go out at the same time, which is unlikely indeed. Like most multi-cylinder motorcycles, XJ's use a wasted spark system. This allows them to run without a distributor. Basically, the ignition timing is controlled based on the position of the crankshaft, and the TCI module fires both of its channel's plugs at the same time; so, 1&4 fire together and 2&3 fire together. For any given firing event, one of the cylinders will near the top of its compression stroke and will have a fuel/air charge ready to be ignited, while the other will be near the top of its exhaust stroke, so firing its plug will have no effect. Again, the point of wasted spark is to make for a simpler ignition system. The spark in the cylinder that's near the top of exhaust is "wasted", but the benefit is that the system doesn't need a cam position sensor or distributor to run. Many recent-model cars also use this configuration (Ford DIS, GM EDIS, etc). Electrically, what's happening is like this: 1. 12V from the ignition fuse on the fuse box is fed to the coil on its Red/White wire 2. The ground side of the coil's primary is either an Orange (left coil) or a Grey (right coil) wire. Yamaha is very consistent about using Orange and Grey for the ignition coil trigger and drive wires in most of its street bike models. The Grey wire is also used for the signal to tach on electronic tach systems. 3. The Orange and Grey wires from the coils go to the TCI box. 4. Under the left-end crankshaft cover (the timing cover), is a reluctor rotor driven by the crank and a pair of inductive pickups. Like the coil drive wires, the pickup signal wires are Orange and Grey, and the Orange pickup wire provides the signal to trigger the ignition channel for the Orange coil drive wire. 5. When the crank is turning, the wide "tooth" of the reluctor will move past the pickups. This induces a voltage pulse, which can be up to 100 volts peak-to-peak, into the pickup coil. This pulse tells the TCI where the crank is relative to firing position and also what the RPM is. Note that this is a pulsed AC signal, so it's not something you can really read with a multimeter... you'd need an oscilloscope to look at the pulse and see whether it looks right. 6. Based on the information from the pickup pulse, the TCI module will charge and fire the coils. The Orange pickup signal is used by the left coil channel in the TCI, and the Grey pickup signal is used by the right coil channel. Again, most parts are separate, so a bad pickup coil or a bad channel in the TCI will stop one pair of plugs from firing but will not affect the other pair of plugs. 7. Charging coils is called dwell. This is something TCI (Kettering induction coils) do, and CDI coils don't do. TCI coils store energy in a magnetic field built up by applying 12V to one wire of the primary winding and grounding the other. Since the 12V is constantly applied to the Red/White wire, it is grounding the other (Orange or Grey) wire that starts dwell. When this "other" wire is disconnected from ground, the magnetic field collapses, and the stored energy gets dumped into the secondary winding. Since the secondary winding has many more turns than the primary, its voltage is much higher (20,000 Volts or more). The "intelligence" involved in the TCI, then, is to, first of all, determine when it's going to need to unground the drive wire and let the coil fire (since this determines timing advance), and then to calulate backwards from there to figure out when to start dwelling the coil. The amount of dwell needed varies based on coil design. For the TCI coils, it's about 3.5 milliseconds. Too much dwell and you could melt a coil or blow the TCI box. Too little dwell, and you don't get a spark or the spark is too weak. This is also why you can't just drop in any old coil to replace a stock one: the coil's resistance, inductance, winding ratio, etc, need to be close enough to stock for the stock dwell times to work. 8. Once the coil is fired, there will be 20KV or more between the two ends of the secondary winding of the coil. The two components of this voltage potential will want to reach each other to complete their circuit. To do this, current will need to flow from one end of the high tension (secondary) winding, through the spark plug wire, through the resistor in the plug cap, across the gap of one plug, through the metal of the cylinder head, across the gap of the other plug, through the resistor in that plug's cap, and up the other plug wire. Yes, the cylinder head is grounded, but, since the secondardy winding of the coil is insulated, chassis ground means nothing here other than another conductor in the current path between the two ends of the high tension winding. The resistors in the plug caps serve not only to reduce electrical noise transmitted by the ignition system, but also to reduce the current flow once the spark is ignited, which lengthens the burn time of the spark. With no resistors, the spark will be more intense, but much shorter in duration. Troubleshooting You'll need a multmeter... preferably a digital one. They're available for as little at $10 from Harbor Freight. 0. The most common electrical problem with these bikes is the fuse box. The fuse clips oxidize and so don't make good contact. If you try to tighten them, they break. If the fuse box is original (glass tube fuses), a best first step would be to swap it for a blade-style box like the ones Chacal carries. 1. Check for spark. Best bet here is to use an extra plug so that all plug holes will still have plugs in them when you're checking. This ensures that the cranking resistance from compression that the starter feels is the same when you're testing as when you're actually trying to start the bike. One by one, pull a boot off a plug and install the spare plug in it. Ground the body of the plug to the engine and crank the engine. Verify whether you're getting any spark. This is best done in shade, as the normal spark on these bikes can be pretty weak. Repeat this for each of the four cylinders and note whether or not you have spark on each one. 1a. No spark on all four: could be lots of things... continue troubleshooting at step 2. 1b. No spark on 1/4 but spark on 2/3, or vice versa. Bad coil, bad coil wiring, bad plug wires/caps, bad TCI channel, or bad pickup coil... go to step 5. 1c. No spark on only one plug... spark on all others. This is pretty rare. It's almost definitely caused by either a shorted to ground plug wire or a bad coil, with the former being more likely. Verify the condition and routing of the spark plug wire. Try swapping plug caps (they screw off, and NGK equivalents LB05F and VB05F are available from most MC shops), or replace the coil. You might want to look up the "coil surgery" article. 2. Verify 12V during cranking. Set the meter to DC Volts. Put the red meter probe to the Red/White terminal at the TCI box (with the TCI box connected). Put the black probe to the Black terminal at the TCI. With the ignition on, this should read 11.5 to 13 volts or so. Crank the engine. This should not drop below 10V or so. 2a. Low or no voltage before cranking: Bad fuse box, bad ignition fuse, Run/Stop switch bad or off, bad ignition switch (key). 2b. OK voltage before cranking, low or no voltage when cranking: Bad fuse box, bad battery (most likely), dirty or loose contacts somewhere along the way, bad or dirty igntion switch or Run/Stop switch, or possibly a bad starter that's pulling down the battery too much. 3. Verify safety cutout (not on 80/81 650's): If the bike has a Black/White wire to the TCI, with the ignition on, but not cranking, set the meter to Ohms and check resistance from the Black/White terminal to ground. It should be 1000 Ohms or more. This terminal is grounded by the safety circuit when the side stand is down and the bike is not in Neutral and the clutch is not pulled in, in order to disable the ignition to keep you from driving with the stand down. The Black/White wire has a bullet connector near the TCI. If a low resistance is found here, you can verify that this is what's disabling ignition by disconnecting the bullet connector and trying to crank again. This should only be a troubleshooting step and not a final fix. 3a. Since the bike should already be in Neutral when doing this check, a failure indicates that the problem is in either the Neutral switch (in which case the neutral light on the instrument cluster wouldn't light either), the sidestand relay, or possibly the diode block. 4. If you've got good 12V at the TCI and it's not disabled by the safety circuit, then the most likely problem really is a just plain bad TCI. Try to find a spare to swap in. They are fairly interchangable, though the "wrong" model TCI will not have the right timing advance curve, so should allow the bike to run but not as well as the correct box would. 5. Isolate a bad ignition channel: The best way to do this is functionally, by switching components between the two channels to isolate what works and what doesn't. Note that, for much of this testing, the timing will be 180 degrees out, so don't expect the bike to run. The point is to see whether the sparking and non-sparking plug pairs switch or stay the same after a check. 5a. Switch the Orange and Grey wires from the pickups (6-position TCI plug) at the TCI. If the sparking and non-sparking pairs of plugs swap (i.e. if you had spark on 1/4 and not on 2/3 prior to swapping Orange/Grey and now have spark on 2/3 and not on 1/4) then you've got a bad pickup. If this didn't make a difference, swap the wires back and go to 5b. 5b. Switch the Orange and Grey wires from the coils (4-position TCI plug) at the TCI. If the sparking and non-sparking pairs of plugs swap, then you've got a bad channel in your TCI. You'll need to replace the TCI or get it repaired. 5c. You've most likely got a bad coil or bad wiring to a coil. Swap the Orange and Grey wires back to their original positions and go to step 6 for more detail on testing the coil. 6. With the ignition on but not cranking, put the meter on DC Volts, put the black probe to the Black terminal of the TCI box and the red probe to the Orange or Grey (depending on which coil isn't working) terminal of the TCI's 4-position connector. You should see 11.5 to 13 Volts. If you do, go to step 7. 6a. Turn off the ignition, pull the tank and disconnect the two-pin connector from the non-working coil. Set the meter to Ohms and check resistance between the two pins of the connector to the coil (this is the primary winding of the coil). This should read about 2.5 Ohms. If it is much higher or infinite then the coil primary is open and the coil needs to be replaced. 6b. If the coil primary does read about 2.5 Ohms, check the resistance from the Red/White pin on the connector that connects to the coil's two-pin connector back to the igntion fuse in the fuse box. This should be very low <1 Ohm. Also check the resistance between the Orange or Grey pin on that connector back to the corresponding pin on the TCI's 4-position connector. This should also be <1 Ohm. If none of this points to a problem, go back and make sure you followed the right steps to get to this point. 7. Remove the plug caps from the two plug wires of the non-working coil. Set the meter to Ohms and measure the resistance from one wire to the other. This should read about 11,000 Ohms. If this is much higher or much lower then you've got a bad wire or a bad secondary winding. You could try the "coil surgery" article to possibly repair the coil, or replace it. 7a. Check the resistance of the spark plug caps. In most cases these should be resistor caps with about 5,000 Ohms resistance from the inner contact to the wire-end screw contact. If they don't read correctly, replace them.