Despite the ah-dang-it sputtering demise of the engine you actually might not have run out of gas.
You'll know this once you unscrew the gas cap and see half a tank of fuel left. Now you know what happens when the fuel pump gives out.
A bad fuel pump or one that's on a slow death march simulates what happens when the fuel tank runs dry. In many respects, you have run out of fuel. Sure, plenty remains in the tank but without a means to an end you might as well be on empty. Additional symptoms of a failed or failing fuel pump include:
- Loss of power
- No starts
- Hard starts
- Cut outs
- Flame outs
- Poor idle
- Lack of rev
Fixing a fuel pump offers no easy task. Most fuel pumps for dirt bikes and ATVs reside inside the fuel tank and include a filter. You need to disassemble the fuel tank which means finding a way to empty the tank of gas assuming the problem started while riding and/or full of fuel. Gas gives off toxic fumes and stinks to high heaven. Don't misunderstand. Gas smells pretty good but in limited, non-concentrated doses. And how about race gas? Mmmm hmmm.
All the pieces of a fuel pump
Anyway, you'll also need to remove the fuel line which requires a specific tool (and we don't carry it) as well as any wires attached to the tank. Finally, you need to take off the small compartment (the pump housing) at the bottom of the tank that holds the fuel pump to the tank. Generally, this has six to eight bolts you need to remove along with a gasket you might as well replace if you plan on digging around.
Once you have the housing out (don't forget which way it faced!) remove the pump from the compartment plate by disengaging the plastic retaining clips or tangs. And be careful not to break them. Find the filter under the pump, remove and replace or change out the entire pump.
Fuel pump separated from its housing
That's fuel pump removal in a nutshell but we can tell you right now don't expect a step-by-step guide on disassembling and repairing the fuel pump. In fact, most problems with the fuel pump belong in the hands of a professional mechanic so we won't blame you if you want to stop now and take your dirt bike to a mechanic. Instead we'll provide an overview of possible issues and you can decide from there whether to DIY it or find that friend or mechanic who knows better.
Fuel pumps have a filter which if clogged prevent gas from getting to the engine thereby mimicking running out of gas and secondarily acting like the fuel pump is shot. So, check the fuel filter and see if it needs replacing. A reputable service manual should have detailed instructions on changing the fuel filter so start there. Clogged filters often result from the use of ethanol based fuels so if you regularly use pump gas with ethanol check the fuel filter.
That's what a fuel filter looks like
Elsewhere, fuel pumps need power to run and use a capacitor. When the engine runs, the capacitor charges off the stator but when the capacitor no longer holds a charge it prevents the pump from running.
Mechanic's Note: When a bike sits for too long the capacitor bleeds off power and can make the bike hard to start.
Sometimes fuel pumps just quit. Tired of life or at least running you around. The quitting fuel pump results from a number of reasons, age being one of them. Once a fuel pump becomes weak it no longer generates enough fuel pressure for the injector to spray fuel correctly. A clogged filter or dying capacitor can affect a fuel pump's operation, as well, diminishing its life capacity. And clogs can develop between the pump and injector affecting the pump's operation.
Diagnosing the problem often gives seasoned mechanics a headache. Injector problems can also mimic fuel pump problems. Newer EFI bikes feature a check engine light on the kill switch that blinks a code indicating the problem but a bad fuel pump might just need a new filter. Today's technology doesn't always offer an immediate and exact solution.
The adventurous tackle the problem and replace the fuel filter or other related parts until such time the entire pump requires replacing. A dying fuel pump usually shows fresh life with a new filter or new capacitor (much like sticking a new battery with an older battery in an electronics device) but eventually quits and needs replacing. A mechanic can also test the fuel pump, capacitor and other related parts to narrow down the issue preventing an unneeded exploration into the fuel tank bowels of your dirt bike and exposing you to carcinogenic and explosive fumes.
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