As the electricity sent from the battery flows through the harness to the electrical components in each part of the motorcycle, it is attenuated slightly at the contact points of each part, such as connectors and switches. If it is a discontinued motorcycle, the wiring of the harness itself may deteriorate over time. Tuning the ignition system to keep the engine going strong is effective, but if the primary voltage of the ignition coil is low, it would be a waste of a high-performance part. In such a case, the direct relay of the ignition coils is what is required to be added.
The further you go to the end of the harness, the lower the battery voltage.
The SPII Full Power Kit by AS UOTANI is a highly trusted ignition system tuning part for discontinued motorcycles. The combination of a high-power ignition coil and control unit generates approximately 40,000 V, compared to the secondary voltage of 20,000 to 30,000 V of the STD coil. In addition, both the discharge current and discharge time greatly exceed those of the STD, which improves combustion conditions with a strong spark. In case the STD is a point type, it also realizes maintenance-free operation by making it contactless.
The high-power ignition coil can be conveniently powered from the factory harness if it is installed in the same position as the OEM coil. However, if you connect the wiring without thinking...
The female terminal connector part, which has come a long way from the battery, is only getting in the 10V range. I haven't tried to find out at what voltage drop the spark stops flying from the plugs, but it sure doesn't feel good. The alternator will continue to generate power when the engine is working, so there is no such thing as a discharge, but with the STD wiring, the headlights are in parallel with the ignition power supply when the headlights are on, which is not desirable from an ignition system tuning point of view.
Electricity is a necessity for motorcycles and cars, which use electricity charged in the battery to power the electrical components of the body. 12V motorcycles are STD when the terminal voltage is 12 to 12.8, and when it drops below this level, the starter motor will not turn, the headlights will dim, and other problems will occur. If the voltage drops below this level, the starter motor will not turn or the headlights will dim.
If the starter motor does not turn, the engine will not start, so the battery must be charged or replaced. Even if the battery is healthy, poor contact or aging of the harness or wiring in the vehicle body can increase resistance and cause the voltage to drop.
One obvious example is insufficient light intensity in the headlights. There are many discontinued motorcycles that are usually lit properly and do not feel dark, but when taken for inspection, they are rejected due to insufficient light intensity. Sometimes, simply replacing the shield beam or STD halogen bulb with an LED bulb will improve the light intensity, but it is common for discontinued motorcycles to have a significant drop in the terminal voltage of the light bulb from 12V to begin with.
The electricity flowing out of the battery goes from the fuse box, through the ignition switch, and in the case of discontinued motorcycles, through the headlight switch to the dimmer switch, and then finally to the headlight bulb. It would be lossy to pass the current required by the headlight through a number of contacts, but that is how many motorcycles were built until the 1970s. That's why we have a bypass circuit that connects the headlight bulb directly from the battery, and the effect of the direct relay is to use the current flowing through the dimmer switch as a switch.
In the case of headlights for inspected motorcycles, there is a specific hurdle of light intensity, and relays that compensate for reduced voltage are effective in clearing this hurdle, but there are other components besides headlights for which voltage drop leads to performance degradation. That is the ignition coil.
The ignition coil boosts the battery voltage by the winding ratio between the primary and secondary coils and then passes a secondary voltage of 20,000 to 30,000 V to the spark plugs. There is no chance to measure whether the spark plug voltage is 20,000 V or 30,000 V, as with a headlight tester, and some people think that if there is a 10,000 V difference, it does not matter as long as the engine does not stop.
However, the greater the magnification during voltage boosting, the greater the difference in secondary voltage will be due to the attenuation of the primary, or battery voltage. assuming a 12V primary voltage of 20,000V, the secondary voltage will drop to just over 18,000V if the primary is 11V at the same magnification. a difference of 2000V may cause spark plug misfires, engine power loss, and even starting difficulties. The difference of 2000V may not cause spark plugs to misfire, engine power to decrease, or even starting to become more difficult. However, it would be a waste if the battery voltage is 12V and the primary side of the ignition coil has a lower voltage than that.
- Point 1: The voltage generated by the battery is attenuated by the harness, connectors, switch contacts, etc., and is not necessarily the same throughout the entire vehicle body.
- Point 2: In the transistorized ignition system, where the battery voltage is boosted by the ignition coil to spark the spark plugs, a slight difference in battery voltage will appear as a large difference in the final voltage.
Add a battery direct relay that switches the primary power supply of the ignition coil.
A power relay used when adding horns and fog lamps, as well as in headlight direct relays. When a small amount of current flows between the blue and black wires, a magnetic force is generated in the coil inside the relay, connecting contacts that can withstand high currents, and current directly connected to the battery flows from the yellow wire to the electrical components. This relay can be used for electrical components up to 12V20A (240W).
Connect the blue wire of the relay to the coil primary wire of the STD wiring, and then crimp the bifurcated wire to the end of the yellow wire of the relay and plug in the SPII High Power Ignition Coil power supply. Since the ignition coil relay is a coupler-on, it can be returned to STD wiring at any time if necessary. Once you see the improvement in voltage drop, though, you won't want to go back to stock.
When the voltage was measured under the same conditions as the STD condition, it increased by nearly 2 V. This is the original battery voltage, and the STD wiring clearly caused the voltage drop. Be aware that even minor corrosion or poor contact of the ignition switch or engine stop switch (kill switch) terminals can cause a voltage drop. If a direct relay is installed, a weak current for activating the relay switch will allow lossless battery voltage to flow to the ignition coils.
The direct relay was installed in the space in the left side cover where the starter relay and coupler are located. It is a small part, but it is very effective in improving the condition of the ignition system.
Although it varies from model to model, discontinued motorcycles with simpler equipment tend to have simpler harnesses. Conversely, the more equipment such as injection and ABS, the more complicated the electrical system becomes. Simple may seem better than complicated, but simple = many things have to be moved at once.
In the case of the Kawasaki KZ900LTD, the primary power source for the ignition coil goes from the battery to the ignition switch, through the connector, and then to the engine stop switch (kill switch). This alone is rather simple, but the wiring after the ignition switch acts like an artery in the main harness, and power for the front and rear brake switches, horn, and indicators in the meter are also branched from here.
Furthermore, the power supplies for the headlight and taillight are also placed in parallel with the primary side of the ignition coil, although they are treated as separate systems with a fuse in the middle.
Because of the connectors and switch contacts, as well as the fact that it shares power with other electrical equipment, there will be a reasonable voltage drop.
The voltage at the primary side of the two ignition coils, which are 4-cylinder, is only 10.3V. Even though an AS UOTANI SPII Full Power Kit is installed to strengthen the ignition system, the voltage of the ignition coils must not be reduced.
The best way to improve these voltage drops is to add a relay dedicated to the ignition coil. Similar to the battery-direct relay for the headlight relay, the relay is placed between the battery and the ignition coil to directly connect the power source. In the case of the headlight relay, a dimmer switch was used as the relay switch, but in the case of the ignition coil relay, the coil power from the factory wiring is used as the relay switch.
Relays for power supply with couplers are easily available at home improvement stores or online, and are easy to install as all you need to do is connect the four wires to the battery positive, body ground, harness for the factory ignition coil that serves as the switch, and the primary side of the SPII, respectively. Do not forget to install a fuse between the battery and relay in case of emergency.
Despite only adding one retrofit relay as part of the work, the voltage on the primary side of the ignition coil increased to 12.29V. Rather, nearly 2V that had been lost in the stock harness was regained.
Unfortunately, I did not notice any obvious change in the maximum power output or the blow-off rate due to the reduced voltage loss (some say that the idling became more stable).
However, there is no single disadvantage to installing a dedicated relay. Rather, it is effective in that it isolates and stabilizes one load for other electrical components by making the ignition coil independent of parallel connections like tachometer wiring.
If you are refreshing or tuning the ignition system by replacing spark plugs, plug cords, or even the ignition unit itself, pay attention to the primary side voltage of the ignition coil and consider installing a buffer relay if necessary.
- Point 1: Direct relays of ignition coils as well as headlight direct relays are effective in reducing voltage drop.
- Point 2: Incorporate a fuse in the power wiring between the battery and the relay.
See KAWASAKI Moto Index Page
See Accessories for KAWASAKI Z900LTD (KZ900LTD)
