outboard motor parts

DIY inboard outboard boat motor parts & accessories

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Standard outboard fuel pump troubleshooting (All brands/models)

There isn't really too much involving fuel pump troubleshooting, and I'm rather amazed at how many fuel pump kits we sell in a years time, as standard outboard fuel pumps don't really act up that much in my experience of 20-some years of wrenching. If you feel though the fuel pump is your problem, read on.

A standard outboard fuel pump is a simple device that operates off the pulse of an engines cylinder. A basic rubber fuel line connects the fuel pump to a pulse valve (some models of fuel pump attach directly to the block with a gasket, sealing pulse passage to cylinder), which is normally threaded into the block with provisions of a clear passage to a specified cylinder. The up and down stroke of the piston in the specific cylinder is what causes the fuel pump diaphragm to flutter, resulting in pumping fuel from tank to carbs.

So how do I know the fuel pump is doing what it is suppose to?
As described above, the fuel pump requires an adequate pulse from the cylinder that it is attached to, so first thing is to make sure compression on that cylinder is up to snuff or the fuel pump can't do it's job. If compression checks out, then next thing is to check fuel pump pressure. All non fuel injected outboard motors operate with a fuel pump pressure of about 5 to 7 psi. If consideribly less than 5 to 7 psi exists between fuel pump and carb/s, the motor is likely to be starving for fuel causing idle and/or upper rpm operation to suffer, not to mention a dangerously lean condition.

So what if everything to do with pulse supply to the pump is good, but I still suspect the pump has a problem?
Although I mentioned not experiencing many fuel pumps actually being bad, it is indeed possible for either the diaphragm, check valves, or other problem to develop in a fuel pump. If it's plainly worn out, then so be it, install a kit or replace pump entirely, but I would suggest checking all other things in this troubleshooter page before just taking it for granted your time and money spent on a fuel pump kit or replacement pump will solve your motor's woes.

Could anything else cause the fuel pump to not provide adequate fuel supply to the motor?
The answer is yes. There could be a restriction or loose connection from tank to fuel pump, amongst other things. Assuming you have no leaks (including pinholes in hoses) anywhere in-between, the following would be things to check for:
  • Fuel tank internal pickup tube clogged, broken off, or otherwise defective.
  • Anti syphon valve located on tank (is so equipped) could be defective (check ball/spring).
  • Any kinked hoses between tank and pump.
  • Defective in-line squeeze bulb (usually the internal check valve).
  • Defective or incorrectly attached fuel line connectors.
  • Clogged fuel filter.
  • Inadequate fuel tank vent or kinked vent hose.

Thats about all there is to a standard outboard fuel pump trouble shooting guide. If you should run across a rare or "quirky" condition not covered here, you are always welcome to contact us with your questions.  Happy pumping!