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  Help, Yamaha 90 Fuel Supply Problem

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Author Topic:   Help, Yamaha 90 Fuel Supply Problem
jstarzy posted 07-10-2009 10:47 PM ET (US)   Profile for jstarzy   Send Email to jstarzy  
The 2003 Yamaha 90-HP two-cycle engine on my 1989 Montauk has been occasionally starving for fuel. While both idling and running at speed it has either sputtered or died. The story:

This spring I replaced the water separating filter assembly after ethanol destroyed the bowl on the previous one I used for 13 years. I also replaced the fuel fittings at the engine and tank. This is when the problem started. But if I connect the motor to the tank directly with the stock Yamaha fuel line, circumventing he filter assembly, lines and connectors, the engine runs fine.

I phoned the filter manufacturer, suspicious of the new filter assembly and was advised to replace the bulb and lines. I did this by installing a new 3/8-inch universal assembly.

After this replacement, the motor is still having difficulty with fuel flow. The vents on the tanks are open and fine.

The new filter assembly has about three hours of run time on it. Is it likely the the filter is restricting the fuel flow?

Last week, when idling, the motor ran the bulb dry and stalled. After pumping it up, the motor started right up and then ran at speed on the river just fine.

Can anyone give me an idea of what is happening? The filter manufacturer is sending a replacement assembly after discussing this with me a few days ago.

Thanks--Jim.

koaman posted 07-11-2009 01:35 AM ET (US)     Profile for koaman  Send Email to koaman     
Have you checked or changed out the fuel line below deck?
seahorse posted 07-11-2009 06:56 AM ET (US)     Profile for seahorse  Send Email to seahorse     
Have you tested the fuel pump? Those are a weak item on Yamahas, especially the ones with the plastic diaphragm.

Also check for any air leaking into the fuel system, use a clear fuel line temporarily at the pump inlet fitting.

jstarzy posted 07-11-2009 10:37 AM ET (US)     Profile for jstarzy  Send Email to jstarzy     
The fuel line below deck (in the Montauk tunnel) has been replaced with a new 3/8 line, head to toe from the tanks to filter to bulb to engine. New clip on connector on both sides.

If there was air sneaking in the system, would the bulb fill and get firm like it does?

Thanks for the responses.

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