Home mechanic (basic tools) ยท Time: 20 to 40 min for an inline filter (estimate); in-tank filters are workshop jobs (estimate)
A fuel filter catches rust, dirt and water before they reach the carburettor jets or the injector. A blocked filter lets the engine idle but starves it at high speed or on hills. Where the filter sits depends on the bike:
- Carburettor bikes: a strainer on top of the fuel tap inside the tank, sometimes a sediment bowl under the tap, and often a small see-through inline filter in the hose.
- Fuel-injected bikes: usually a strainer on the pump inside the tank, and sometimes a separate high-pressure filter. The K-Light 125 has a petrol filter and a pump strainer in the tank.
Safety
- Outdoors or well ventilated, engine cold, no flames or sparks, extinguisher at hand, safety glasses on.
- Fuel-injected bikes: do not open a pressurised line at home. The K-Light 125 manual warns that residual pressure can spray fuel when the hose comes off. Filters inside the tank or on the pump are a workshop job.
You need
- A filter that matches the hose size and flow direction. Paper filters for injected systems are rated for pressure; do not fit a cheap carburettor filter in a pressure line.
Steps (inline filter on a carburettor bike)
- Turn the fuel tap OFF.
- Note the arrow on the old filter. It points toward the engine.
- Put a rag under the filter. Slide the clips back and pull the hoses off one end at a time. Let the fuel drain into the jar.
- Look at the old filter. Rust flakes mean the tank is rusting: see Rust or flakes inside the fuel tank. Water droplets: see Water or dirt in the fuel.
- Fit the new filter with the arrow toward the engine. Keep the hoses free of kinks and away from the exhaust.
- Refit the clips over the hose where it covers the filter spigot.
- Turn the tap ON and watch every joint for a minute. No drips allowed.
Steps (tap strainer)
- Drain the tank first (see Drain old or contaminated fuel).
- Remove the tap from the tank. Clean the strainer and any sediment bowl by blowing air from the inside out, or fit a new strainer if it is torn.
- Refit with a new gasket or O-ring, and do not overtighten. Check for leaks, then follow Check the fuel tap, lines and flow.
Fuel-injected bikes: what to ask the workshop
- Replace the in-tank filter or pump strainer with a new pump seal ring, and check the tank for rust while it is open.
- Check fuel pressure after the job against your bike's value.
How often
Follow your bike's service schedule. The K-Light 125 manual gives three different fuel filter intervals in different places (PDF pages 51, 274 and 275), so no single figure is given here. Change the filter early after any rust, water or dirty fuel.
Check your work
- No drips, no fuel smell, filter arrow toward the engine.
- The engine pulls cleanly at full throttle on a road test.
If it did not fix the problem
- Still starving: check the tank vent, then clean the carburettor or check the fuel pump.