Harley Davidson's 883 Sportster model has been part of their range since the late fifties. Though the overall technical information and styling has remained the same, countless tiny edits and improvements have been made to the bike's power plant, in an attempt to squeeze every bit of performance and efficiency from it. Increasing the potential power of the engine also means the risk of increased wear on its components. A rev limiter can prevent this by cutting ignition above the point in the RPM range at which the engine can function consistently, without excessively wearing its components."
An RPM limiter is fitted to most modern motorcycles when they leave the factory, this is for a number of reasons. The first is to prevent rapid or excessive engine wear. Pushing the engine up to or past its limits causes the valves to rapidly bounce up and down as they let air in to the engine. Running them too fast reduces the strength of the springs that return them to position. This causes them to "Float" in the half-open position, interfering with fueling and timing. Other motorcycles, such as Suzuki's Hayabusa, include a limiter because without one, they would be capable of frankly irresponsible speeds.
The Sportster's limiter is set between 5200 to 7000 RPM at the factory, depending on the particular model. This has been determined as the upper range at which the engine can function consistently, without excessively wearing its components. The limiter is governed by a unit attached to the digital fuel injection module, regulating the engine timing to automatically reduce the RPM level if it gets too high. The sensation of the modulating acceleration in this range is referred to as "Bouncing off" the limiter
Aftermarket ignition modules can be fitted that allow the adjustment of the limiter settings. The new module either contains onboard controls or includes a port that allows connection of a laptop running interface software. Some modules allow the removal of the limiter, other just allow the user to adjust the threshold at which it kicks in. The second variety is more advisable as it allows the generation of more power, while still retaining the engine protection of the original design.
If the limiter is adjusted or removed via the use of an aftermarket unit, it is normal to notice some issues with timing, fueling and aspiration. This is because the original fuel injection settings are configured in line with the peripheral components that surround it. The air filter and exhaust baffles may have to be replaced in order to provide the necessary airflow to the injector, once the new limiter settings have been applied.
The Sportster is available with one of two different engine sizes; 883cc, or 1200cc. According to HD's distributor in the UK, all of the bikes within each category have the same 5200 to 7000 limiter settings. Though the bikes feature different frames and wheels, the engine, gearbox, valvetrain and electronics are identical.
- HarleyDavidson.com : 883 Specs, Metric.
- Harley Davidson Sportster Performance Handbook, Buzz Buzzelli, 1997
- Photo Credit Jupiterimages/Photos.com/Getty Images
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