The Vulcan 750, like many motorcycles, has an air inlet designed to allow air into the exhaust system. This system provides purely for cleaner exhaust purposes, and provides no useful benefit to the operation of the vehicle. Combustion in the engine cylinders takes place as long as there is sufficient oxygen to fuel the combustion process. When the oxygen is depleted, further combustion ceases. As the combusted exhaust leaves the engine cylinders, there is sufficient fuel in the exhaust to support further combustion. When air is allowed into the exhaust by the inlet valve, the still hot exhaust gasses, now fueled by additional oxygen, ignite, re-commencing the process of combustion.
This process more fully burns the exhaust fuel and thus minimizes carbon monoxide emissions through oxidation, converting carbon monoxide to harmless carbon dioxide. While this process certainly reduces the emissions of the motorcycle, it is not completely a benevolent process. Because combustion is occurring in the exhaust chamber, there is significant heat buildup in the exhaust system. This leads to a hotter engine running temperature, hot exhaust pipes, and premature wear on the exhaust system metals, most visibly recognizable as exhaust pipe bluing. Additional side effects of this secondary combustion include frequent backfires and common engine rumbling.
The only solution to this problem is to effectively seal the air intake valve to the exhaust chamber. On the Kawasaki Vulcan 750 and most other models, the air intake system is comprised of a reed valve connected to an air suction valve. The purpose of this system is to allow fresh filtered air to the reed valve, but prevent any dirty exhaust air from returning to the air cleaner, thus becoming available to the air intake for the fuel mixture. Installation of the Coasters prevents any air from entering the exhaust system by replacing the reed valve assembly with a solid plate, thus sealing up the inlet to the exhaust system.Installation on my bike took less than fifteen minutes. While removal of the air suction valve assembly and the reed valve housing cover can also be done, as these components are effectively disabled, I chose to leave mine in place, making it easier for me to reinstall the reed valve assembly if I ever needed to.
Pictures of the installation to be made available shortly.
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