Fuel pump

How it works

On a fuel-injected bike, the fuel pump usually sits inside the tank, often as part of a module that also holds the fuel gauge sender and a filter. It sends fuel at constant pressure to the injectors, with the pressure held by a regulator. When you switch on the ignition, you often hear it whirr for two or three seconds: it is pressurising the system before starting. A weakening pump gives an engine that lacks top-end power, stutters under load or stalls; a dead pump prevents starting altogether. The pump's filter can also clog, especially if the bike often runs on reserve or the fuel was dirty. Some carburettor bikes also have a small electric or vacuum pump when the tank sits lower than the carburettor. The check is done with a fuel-pressure gauge, against the manual's value, after checking the pump fuse and relay.

Maintenance tips

• ✓Switch on the ignition and listen: the pump should whirr for a few seconds; if not, check the fuse and relay before the pump.
• ✓Avoid running on reserve all the time: the pump is cooled by fuel and picks up deposits from the bottom of the tank.
• ✓Replace the fuel filter at the interval in the manual.
• ✓Fuel pressure is measured with a gauge: it is the only reliable way to judge a pump.
• ✓The injection system stays under pressure: depressurise it as the manual describes before opening a hose, away from any flame.