The Sportster 1200 is a small, agile motorcycle propelled by Harley-Davidson's 1200cc Evolution v-twin motor. For most riders, the power provided by the motor is more than adequate. However, the Sportster's motor can begin to feel slightly subdued after a while, sending its owner in search for more power. Most methods to maximise your Sportster 1200's potential can be performed in your own garage using basic hand tools and involving the replacement of stock components. Major motor work and tuning, however, requires extensive, and costly, mechanical work.
Replace the stock air intake system. The factory-equipped air intake system is restrictive, allowing a smaller amount of air into the carburettor. While this lowers emissions, power is also reduced. Removing the stock air filter and intake and replacing it with a free-flowing high-performance intake and air filter will allow an increased amount of air into the carburettor for stronger combustion and more power.
Replace the stock exhaust system. The exhaust system, like the air intake, is also designed to reduce emissions, both gaseous and audible, through the use of smaller-diameter exhaust pipes and baffles. Installing a free-flowing performance exhaust system, which includes an increasing diameter along the length of the exhaust pipes, and less-restrictive or removable baffles will improve the flow of exhaust gases, increasing power.
Rejet the carburettor. As supplied from the factory, the carburettor on your Sportster 1200 uses a series of nozzles, or jets, to meter a specific amount of fuel into the air pulled in from the intake system to create the air/fuel mixture required to power the motor. This mixture is set leaner, meaning there is more air than fuel in the mixture, to reduce emissions. Unfortunately, this lean condition also robs the motor of power. Replacing the carburettor's jets with larger jets will add more fuel into the air/fuel mixture, making it richer and increasing the power of the combustion. This step is mandatory after replacing the air intake and exhaust systems to compensate for the additional amount of air travelling through the motor.
Replace the stock drive (front) pulley. A Sportster 1200 is equipped with a 29-tooth drive pulley that pulls the drive belt to turn the rear wheel's driven pulley. This allows for decent acceleration while providing more comfort while riding at motorway speeds above 88.5 km/h (55 mph). Replacing the drive pulley with a 27-tooth pulley from an 883 Sportster will dramatically increase acceleration, but it will make the engine work harder and reduce comfort while at motorway speed.