The secondary air injection system [A] helps Kawasaki keep motorcycle exhaust gases below the established emission regulation limits. This system draws air into the exhaust ports, dilutes and burns harmful ingredients in the exhaust gas in order to reduce them. This allows the carburetor to be set at a reasonable setting position without adjusting it much leaner, so engine performance and actual riding performance are not spoiled.
But, under the trend that the emission regulation becomes more severe, Kawasaki has adopted two catalytic converters [B] in addition to the secondary air injection system. Moreover, a BDSR 36—type carburetor has been adopted because of its good balance between cost and performance. As a result, we can reduce the exhaust gas emission below the current standards without hurting the output performance and the actual riding feeling at all. The harmful ingredients in the exhaust gas are reduced considerably under running performance of emission regulation like LA4 or EC mode. As actual examples, carbon monoxide (CO) is reduced about 70%, hydrocarbons (HC) about 60%, nitrogen oxides (NOx) about 10%.
Moreover, in order to improve the reliability of the system, we install fuel cut valves [C] as a catalyst protection system.
Exhaust gas after purification
Kawasaki low exhaust emission system
1. Exhaust Purification System
The burned gas, which goes out from the combustion chamber, is injected with secondary air (adding necessary oxygen), and is cleaned up while passing through two small catalytic converters in the joint pipe and the main catalytic converter in the silencer, and then goes out to the atmosphere.
Secondary air injection system
1) In order to oxidize CO, and HC by the catalysts, the proper amount of oxygen is necessary. As original combustion gas has little remaining oxygen, air is injected in the exhaust ports by the secondary air injection system in order to supply enough oxygen to the combustion gas to purify CO, and HC to a certain extent as well as prepare for activation of the catalysts. Since the carburetor is set at richer level [A], and air/fuel mixture (A/F) is about 11-14, NOx is at lower level from the beginning as shown in the figure. And, A/F becomes lean (about 13.5-15) after the combustion chambers owing to secondary air injection and combustion.
Exhaust gas before purification
2) Precatalytic Converters [A].
A small-size three-way catalytic converter (precatalytic converter) is installed in the pipe ahead at the joint [B] of the silencer. A precatalytic converter is made of a punched metal pipe [C] of stainless steel, and its surface is covered with alumina upon which platinum and rhodium as catalysts are applied. Generally, the temperature of the exhaust gas must be higher than the activation temperature, so we set this precatalytic converter at the upper portion of the main catalytic converter where the temperature of exhaust gas is high. Accordingly, the precatalytic converter will be activated even under low load conditions. Activation of the precatalytic converter raises the exhaust gas temperature by the catalyst reaction, which helps the main catalytic converter operate more efficiently. The precatalytic converter purifies CO, HC. and NOx to a certain extent.
3) Main Catalytic Converters [D].
The converter is a three-way catalytic converter upon which platinum and rhodium are applied, and has a cylindrical metallic honeycomb structure [E] made by bending a corrugated sheet and a flat sheet of stainless steel into a spiral of increasing diameter. The main catalytic converter is installed in the first expansion chamber of the silencer. When the exhaust gas passes through the upper portion of the secondary air injection system, the precatalytic converter, and the inside of the honeycomb, the main catalytic converter works efficiently to reduce CO, HC. and NOx. So, we can keep it within regulation.
The honeycomb structure is convenient for the catalytic converter because it has a large surface area but small size to react effectively and has low exhaust resistance. In addition, its inherent strength helps resist vibration, and has simple structure welded directly on the silencer.
Catalytic converters
2. Catalyst protection system
When excessive unburned gasoline flows more than the allowable amount into the exhaust gas during running, the temperature of the catalysts rises abnormally because the unburned gasoline reacts with heated catalysts (at the activation temperature or higher). In an excessive case, the problem such as melting-down occurs. Moreover, there is a possibility that the purification performance becomes poorer when it is cool (below the activation temperature). So, the fuel cut valve [A] as a catalyst protection system is installed on each carburetor float bowl [В]. It runs by the IC Igniter and opens and closes the fuel passage toward a main jet [С]. A catalyst protection system works in the following cases.
1) Prevention of unburned gasoline from flowing when overspeed limiter works.
The limiter has fuel cut-off and ignition cut-off operations.
2) Prevention of unburned gasoline from flowing when the engine stop switch is turned off during running.
When the engine stop switch is turned off while coasting the motorcycle, fuel is cut off. For example, fuel is cut off under the abnormal running condition that you go down the slope with the engine stop switch OFF.
3) Prevention of unburned gasoline from flowing when misfire occurs by a cutoff of a primary coil in a stick coil.
Fuel is cut off when an electric current of a primary coil becomes abnormal because of a cutoff of the primary coil when the engine is running.
4) Prevention of solenoid valve lock
If a driver always runs the engine under the red zone in the tachometer, the IC igniter doesn't operate overspeed limiter and the catalyst protection system doesn't have a chance to work. The old fuel may gum up the fuel cut valves which remain seated in the float bowls. To cope with, the IC igniter test-operates the fuel cut valves when starting the engine and prevents lock of the valves.
5) Usage of leaded gasoline is prohibited completely,
Leaded gasoline harms the purification efficiency of the catalysts.
The performance of the catalyst protection system is summed up as follows.
Fuel cut valve
Performance of catalyst protection system
| № | Running condition | Ignition switch | Engine stop switch | Protection system | Fuel cut valve | Remedy (Action) |
| 1 | Normal | ON | ON | OFF | OPEN | • Not necessary (Normal condition) |
| 2 | Overspeed performance | ON | ON | ON | CLOSE | • Not necessary |
| 3 | Abnormal (misfire) • Defects at the stick coil primary-side | ON | ON | ON | CLOSE | • Inspect the connection at the primary-side of the stick coil. |
| 4 | Abnormal (misfire) • Defects at the stick coil secondary-side • Battery is dead. • Spark plug fouling • Defects of the pickup coil • Defects of the IC igniter • Defects of the carburetor | ON | ON | OFF | OPEN | • Inspect the stick coil. • Charge the battery. • Clean the spark plug and adjust the gap. • Inspect and replace the pickup coil. • Inspect and replace the IC igniter. • Inspect and adjust the carburetor. |
| 5 | Abnormal (no spark) • Short of the engine stop switch • While coasting the motorcycle, do not turn the engine stop switch OFF. | ON | OFF | ON | CLOSE | • Inspect and repair the engine stop switch. • Turn the engine stop switch ON, and run. |
| 6 | Abnormal (no spark) • Short of the ignition switch • While coasting the motorcycle, do not turn the ignition switch OFF. | OFF | ON or OFF | OFF | OPEN | • Inspect and replace the ignition switch. • Turn the ignition switch and the engine stop switch ON, and run. |
3. Maintenance
Special maintenance is not necessary except for the inspection of the air suction valve (which has been described in this manual).
1) Replacement of Muffler Assy
It is impossible to replace only catalytic converters because they are welded In the muffler. So, in the following case, the replacement of the muffler assy is also necessary.
- In case of using not-appointed fuel (leaded gasoline, etc).:
- Purification efficiency decreases in a very short period because lead poisons the catalytic converters. Although the appearance of the converter and engine performance are not effected, the replacement of a muffler assy is necessary to secure the purification efficiency of exhaust gas.
- In case catalytic converters melt down by overheating: Especially in the case that a lot of unburned gasoline flows into the catalytic converters under the extreme running condition far beyond common sense, there is a possibility that the catalysts overreact and that catalytic converters overheat severely. If they melt down, it causes poor engine performance, deterioration of emission noise level, and purification efficiency. So, the muffler assy must be replaced.
2) Durability.
It has the same durability as a conventional muffler.
3) Disposal to Waste.
As any harmful toxic substance is not used especially, it can be disposed as usual industrial wastes. The body of the muffler is made of aluminum steel. The catalytic converter is also made of stainless steel which has alumina on its surface, and the main ingredients of catalysts are platinum and rhodium.
4. Handling precautions
Catalyst protection system against mishandling is applied to a vehicle with catalysts. But, we prohibit depending on the system too much when running.
1) Use only unleaded gasoline: Usage of leaded gasoline is prohibited completely. Only fuel and additives which are specified in the Owners Manual can be used.
2) Use specified engine oil which is described in the Owner s Manual: In case of some ingredients which give bad effects to the catalysts (such as phosphorus "P", lead "Pb", sulfur «S») are included, the purification efficiency decreases.
3) Coasting (such as cranking while going down a slope) is prohibited with the ignition system OFF: The engine running without igniting causes a great flow of unburned gasoline and the decreasing of purification efficiency, and melting down of catalysts at the activation temperature or higher.
When the ignition switch [A] is turned off, the fuel cut valves [B] do not work. So. avoid coasting with the ignition switch OFF.
Do not run the engine nor coast the motorcycle under the misfire which occurs by defects such as a bad connection with the spark plug at the secondary wiring of the stick coil [С].
Do not coast too much with the engine stop switch [D] OFF. Under the condition that the engine stop switch is turned off during running, the IC igniter [E] closes the fuel cut valves to shut off fuel.
Do not run the engine nor coast the motorcycle too much under the condition that the primary wiring of the stick coil does not connect completely (misfire). Incomplete connection or cut-off of the primary coil makes the fuel cut valves start to cut fuel. In this case, from the standpoint to protect the catalysts, the fuel for all cylinders is cut off even if one cylinder has been affected.
Kawasaki low exhaust emission system
Do not run overspeed limiter too much from the standpoint to protect the engine. (Overspeed limiter has a protection system that applies ignition cut method and fuel cut method together. Conventional system applies fuel-on method).
Do not run the engine even if only one cylinder has a misfire or has unstable running. In this case, request the nearest service facility to correct it. If you have no choice but running by yourself, keep engine rpm as low as possible and try to finish running at the shortest period.
When the battery is dead, do not push-start. Connect another full-charged battery with jumper cables, and start the engine.
5. Additional information
1) Secondary Air Injection System
The mechanism is simple and power loss is minimum because the system uses the vacuum pressure created by exhaust pulses.
The secondary injection air helps the fuel/air mixture burn more completely (Primary air means air which flows through the inlet pipe). As the exhaust valve opens, and the burned fuel passes the exhaust valve, a stream of fresh air is introduced through the air suction valve. This fresh air burns the unburned gas and converts the carbon monoxide (CO) and hydrocarbons (HC) into harmless catbon dioxide (CO2) and water (H2O).
CO + 1/2 O2 → CO2
НС + O2 → CO2 + Н2О
The secondary air injection system consists of a vacuum switch valve, and two air suction valves. Without using an air pump, the air suction valve can draw fresh air into the exhaust passage near the exhaust valves by vacuum that exhaust pulses generate.
Air suction valves
The air suction valves is a check valve which allows fresh air to flow only from the air cleaner via air hoses into the exhaust port and prevents return flow. Remove and inspect the air suction valves periodically (see Engine Top End chapter in this Service Manual). Also, remove and inspect the air suction valves whenever the Idle speed is unstable, engine power is greatly reduced, or there are abnormal engine noises.
Vacuum switch valve
Although the vacuum switch valve usually permits secondary air flow, it closes when a high vacuum (low pressure) is developed at the inlet pipe during engine braking. This is to shut off secondary air flow and prevent explosions in the exhaust ports which might be caused by extra unburned fuel in the exhaust during deceleration. These explosions, or backfiring in the exhaust system could damage the air suction valves.
Regular inspection of the vacuum switch valve is not needed. If backfiring occurs frequently in the exhaust system during engine braking or if there are abnormal engine noises, check the vacuum switch valve as described in the text (see Engine Top End chapter in this Service Manual).
Secondary air injection system
1. Air cleaner housing; 2. Air hose; 3. Inlet silencer; 4. Vacuum switch valve; 5. Air suction valve; 6 Exhaust valve; 7. Carburetors; 8. Inlet pipe; 9. Inlet valve
2) Operation of three-way catalytic converter.
The three-way catalysts are used for the catalytic converters and the main catalytic converter. These converters can clean up carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) at the same time.
CO and HC are oxidized (O is added) by platinum (Pt) and converted to harmless carbon dioxide gas (CO2) and water (H2O), and then the exhaust gas is cleaned up:
CO + 1/2 O2 → CO2
НС + O2 → CO2 + H2O
NOx is reduced (O is removed) by rhodium (Rh) and converted to harmless nitrogen (N2) and oxygen (O2), and the exhaust gas is cleaned up.
NOx → N2 + O2
Main catalytic converter
3) Property of catalyst.
Most catalysts are powders of metal or of metallic compounds, and they increase the rate of a chemical reaction.
Catalysts are supposed to act in some way to loosen the bonds of the reacting substances. In other words, they lower the energy of activation, thus allowing the reaction to proceed more rapidly. To activate catalysts, the temperature of the exhaust gas must be higher than the activation temperature that is 220-230°C for new catalysts, and 270-280°C for used catalysts (after 10000-20000 km ride).
The catalyst itself undergoes no permanent chemical change, or can be recovered when the chemical reaction is completed. So, the muffler with built-in catalyst has the same durability as the conventional muffler.
The mechanism of catalytic action is supposed to be a surface phenomenon in which reactants are absorbed onto a small portion of the surface of the catalyst. The catalytic converter is made of stainless steel and the surface is applied by alumina (aluminum oxide Al2O3). The alumina adheres to the stainless steel wall and the catalyst adheres to the alumina very well. The alumina surface is not uniform and there are corners, edges, dislocations, and grain boundaries. Catalyst is applied on the alumina and this makes the catalyst surface rough. The rougher the surface is, the more actively the catalyst adsorbs the reactants.
If various impurities like lead are adsorbed, they block the small portion of the catalyst surface, preventing absorption of CO, HC, and NOx. This is the reason why leaded fuel poisons the catalyst without any break on the surface or generation of heat.
Catalysts are generally efficient in small quantities. A catalyst can catalyze the reaction of several thousand to a million times its weight in reactants. The three-way catalyst is a blend of platinum (Pt) and rhodium (Rh) which are expensive. But a converter uses only about 0.05 gram of Pt and 0.01 gram of Rh and a main catalytic converter uses only about 0.4 gram of Pt and 0.1 gram of Rh.
