Why Is My New Fuel Pump Not Working?

Rick Sosebee
by Rick Sosebee
The ATV AnswerMan helps out a Rhino owner having some fuel trouble

Why is my new fuel pump not working? This is more or less what one of our readers wants to know and the ATV AnswerMan is on the case.

Here is exactly what reader Scott asked the ATV AnswerMan, followed by his answer:

I have a 2006 Yamaha Rhino 660 that I had a new fuel pump put on recently. I only rode it a few times and now it will not crank. It will turn over but acts like not getting fuel. I checked fuel filter because its right below fuel pump no gas in filter does this mean new pump went out or what can I do or check to make it crank?

The fuel pump you are referring to is a diaphragm-style pump. It only has thin gasket-type materials that flex and “siphon” the fuel through from the tank to the carburetor. These pumps are pretty reliable and I would say having it simply drop out after only a few uses is rare. So let’s look at a few things first. Be sure to search all of the lines attached to the pump for cracks; some of these can be small, maybe not even evident until pressed or pinched between your fingers. Air leaks are your enemy.

If this were in my shop, I would pull the center cover breather inlet (should be twin Phillips head screws) and simply place my hand over the mouth for the air box. This would create vacuum on the engine intake thus effectively choking the engine. This should also pull fuel from the tank provided everything is functioning properly. The inline fuel filter may not always have fuel in it when the machine is idling or even simply sitting with the engine off. Pulling the passenger seat out will give you a clearer view and help you monitor the fuel climbing up through the fuel filter.

If this provides fuel up into the air box then you know the pump is potentially working. The engine should attempt to start over and at the first sign of a start pull your hand off of the air box so you do not flood the engine. If this works then I would keep searching for a leak in the fuel system between the carburetor and the tank that allows the fuel to run back down after startup. There is a roll over valve assembly inline from the tank that could be giving some trouble like a check valve as it essentially cuts off air flow through the vent lines to prevent the fuel delivery if you were to turn the unit on its side. Sometimes the ends of these little pipes are great storage homes for “Mud Dauber” bees and a clogged vent line is bad.

Finally, If all of this proves to be good but the unit still will not start, I would pull the spark plug out of the cylinder head, place it in the spark plug boot (as it would be in the motor) and gently place it against the engine with the probe or “sparky end” touching the side of the engine as a ground. Then have someone turn over the engine. Be sure you do not crush the ground electrode or the “little thingy” that stretches out over the center electrode, as this will cause performance issues with the engine when it does get running. I’m sure you know you need fuel AND spark, so be sure you’re getting a good fat blue ark on the plug. Please let us know how this turns out as the audience is in suspense!

Rick Sosebee
Rick Sosebee

Whether he is in Mexico covering the Baja 1000, building ATVs for local racers, or out enjoying the trails, Rick’s passion shows in his stories. Learning to wrench his own machines from his grandfather, Rick also has an undying appreciation for the mechanics of off-road vehicles. Do not let the dirt and mud fool you, though, as Rick also has a deep love for street cars.

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