1983 Yamaha xj650 troubleshooting?

Before you start replacing parts in your ignition system, use the handy references below to evaluate the main ignition system components: the pick-up coils, the TCI box, the ignition coils, the spark plug caps, and the spark plugs.

The following lists specify the resistance values of the spark plugs, the spark plug caps, the ignition pick-up coils (which are located behind the left side round crankshaft end cover), and the ignition coils. The resistance of the pick-up coils can be checked at their connector to the TCI box by measuring the resistance between the grey and the black wire (this checks the condition of the first pick-up coil) and then between the orange and the black wire (this is the resistance of the other pick-up coil).

The TCI "black box" units, unfortunately, are not designed to be "tested" in a simple manner.

Remember: when checking electrical components for their resistance values, it's not just the resistance of the component itself, but also of any sub-harness wiring leads which may factor into the resistance readings! The component itself may be electrically "good", but if the wires or, more likely, the wire end metal terminals are corroded, looses, etc..........then the problem with the wire or the terminal also becomes a problem for the component, too.......

NOTE: "K" is abbreviation for a thousand units, so "5K" ohms = 5,000 ohms of resistance, etc.

XJ650 models:

Pick-up coils:
1982-84 XJ650 Maxim: 650 ohms +/- 20% = 520 ohms to 780 ohms acceptable range
1982-83 XJ650 Turbo: 120 ohms +/- 20% = 96 ohms to 144 ohms acceptable range

Ignition Coils:

Primary side (input from main wiring harness):
2.5 ohms +/- 10% = 2.25 ohms - 2.75 ohms acceptable range

Secondary side (spark plug wires, without their end caps):
11K ohms +/- 20% = 8,800 ohms - 13,200 ohms acceptable range

Spark plug caps:
5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range

Spark plugs:
0 ohms per plug


TCI Units:

Yamaha (thankfully!) used a TCI (which stands for Transistor Controlled Ignition) system on all XJ-series bikes to control the coils, timing, spark advance, etc. A TCI unit is an "early" version of the now-common electronic control systems that are used on virtually all modern vehicles of almost every type, and even these early versions are completely maintenance-free and very rarely cause problems...........which is a good thing, because original TCI boxes are no longer available new.

When engine performance problems develops, many people immediately suspect that the cause may be within the "black box" workings of their TCI unit, which is unlikely. The factory service manual gives "instructions" for diagnosing TCI problems, and it basically says "test every other possible cause for your problem and if no other cause for the problem exists, only then should you "suspect" TCI failure, but before you buy a replacement, first try to find a known, working TCI unit from a similar bike and plug it in on the problem bike, and see if the problem goes away............"


There are three main problems that TCI units succumb to after years of reliable service:

1) bad solder joints on some of the internal components (known as "cold solder joints") result in the component pieces coming loose from the circuit board, and thus they can no longer perform their function reliably (or at all).

2) component failure......a blow-up capacitor, a fried transistor, a burned circuit trace, etc. This situation can develop if you have a short-circuit in your electrical system, or hook up your battery or jumper cables incorrectly, etc. TCI units do not like "big blue sparks" in the electrical system (except at the spark plugs, of course!).

3) dirty external terminal connections.

Bad solder joints can be repaired by someone who is skilled at that sort of diagnosis and repair, and even individual circuit components can be replaced, but it's tough to find someone in the modern world of "pitch-and-plug" skill-sets who actually has the skill and patience to do this type of work. Yamaha gave absolutely "zero" electrical specifications for checking the condition of the TCI units, besides the afore-mentioned "check everything else first" type of diagnosis.

But you can perform a simple set of tests to determine whether your TCI unit is good or not, without having a second, known good unit to install in place of the suspect unit. Although these instructions were written for XS owners, the exact same thoughts apply to the TCI units on the XJ-series of bikes:


All of the XJ-series TCI units are of the "4RO" style as described in the above article.

And if the above isn't enough, if you feel the need to get medieval with your TCI unit, well, then it doesn't get much better than this:


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