Troubleshooting Yamaha Outboard Fuel Pump Issues
An outboard that doesn't run smoothly, fails to deliver maximum power and struggles to idle could be experiencing fuel pump problems.
Below we run through a few troubleshooting tips to help you diagnose a faulty fuel pump. Watch our Yamaha Outboard Fuel Pump Issues video above — in which we guide you through an outboard's fuel system — to troubleshoot possible issues that may be causing fuel pump problems.
NOTE: Although we're using a Yamaha 250HP motor as an example, the fuel system will be very similar on any modern outboard, regardless of brand or model.
How a Modern Outboard Fuel System Works
Modern outboard motors have complex fuel systems. Gone are the days of a gravity-fed fuel line leading from the fuel tank to a carburetor.
A modern outboard fuel system will typically consist of the following:
Primary fuel filter: The cup filter located on the side of the motor that sits between the fuel tank and the low pressure fuel pump.
Low pressure fuel pump: Draws fuel from the fuel tank and sends it on toward the engine.
Vapor separator tank: The VST is the unit that houses another fuel filter and fuel pump.
VST filter: The fuel filter within the VST that further filters the fuel before it enters the high pressure fuel pump.
Secondary fuel filter: In-line filter that separates even smaller contaminants from the fuel before it enters the VST.
High pressure fuel pump: Also known as the VST pump, it pressurizes the fuel before sending it to the fuel rail.
High pressure fuel rail: Takes the pressurized fuel and delivers it to the fuel injectors. The fuel must be at a precise pressure for the fuel injectors to perform correctly, and thus the engine to run at its peak.
Because working on the VST tank and its internal fuel filter and fuel pump requires specialist tools and equipment, fixing it should be left to your local dealership. All you need to keep an eye on and periodically service are the low pressure fuel pump, the primary fuel filter and the secondary fuel filter.
Troubleshooting Outboard Fuel Pump Problems
When people talk about the fuel pump on an outboard, they’re referring to the low pressure fuel pump mounted on the side of the motor.
The fuel pump has one job, and that’s to pump fuel from the fuel tank to the motor. If the fuel pump isn’t working properly, the engine won’t either. As such, if a faulty fuel pump isn’t supplying enough fuel to the motor, the engine won’t achieve wide-open throttle (WOT) and may stall when idling.
Because the fuel pump is a self-contained unit that can’t be dismantled or serviced, you’ll need to replace it with a new fuel pump assembly. However, before buying a new fuel pump, check the pump’s electrical connections and that the pump is getting power. The problem might just be a blown fuse that needs to be swapped out.
Troubleshooting Outboard Fuel Filters
A blocked fuel filter can slow or reduce the amount of fuel reaching the engine.
Troubleshooting Outboard Fuel Lines
When you’re checking the fuel filters, give the fuel pump’s inlet and outlet fuel lines a close inspection too. If you see any leaks or there are worn or damaged fuel pipes, you should replace them immediately.
Finding Outboard Fuel Pumps, Filters and Lines
Boats.net carries thousands of OEM fuel system parts. Simply select your outboard’s make, year, HP and model, and pick the OEM parts you need for your engine.
For example, on the Yamaha 250HP LF250TXR outboard parts page, click on Fuel 1 to find the primary fuel filter; click on Fuel Injection Pump 1 to find the fuel pump; and click on Fuel Injection Pump 2 to find the secondary fuel filter.