Twin Yamaha f70 bogging down

[Nicturner808]

Bought a boat that didn't get used very often. Then after running it for 20hrs or so one of the engines starting sputtering and losing rpms regularly. I could pump the fuel ball and get it back and running. Eventually it got worse and the the second engine started doing it. Can get them to run but eventually they just bogg down. It happens in high and low speeds. Not sure where to start. The fuel water separator and fuel filter are not old, but I think the problem is elsewhere. Both check engine light came on the last time I ran it and barely made it back to ramp after pumping bulb and starting over and over. Would run for a min and then stall out. Any direction and advice would be greatly appreciated.
Fyi the engines only have 100 hrs on them and they are 2011

[fairdeal]

with both engines affected, clearly is either a fuel supply or a fuel quality problem

are both engines drawing off a single built-in boat fuel tank?
you say "the" fuel water separator - singular?
that itself would seem problematic - once there is any restriction in the filter

if "pumping the fuel ball" temporarily lets the engine run fine -
that makes it a supply problem before the VST

but I'm not sure that's exactly what you are describing

and the "check engine light" ? you got me there
now, if that was a WIF light....

[rodbolt17]

sounds like water in the fuel.

[Nicturner808]

I meant there are two fuel separators. And there is an engine image on both gauges. I only use ethanol free gas and has been ongoing issue slowly getting worse and put a fresh 20 gallons in prior to both engines cutting out. Not sure where to start?

[99yam40]

adding fresh gas to old bad gas makes more bad gas.

If the old gas was bad or has water in the tank , adding fresh does not help much

WIF (alarm/light)means water in fuel in case you did not get that.

have the fuel pressures monitored to see what is going on
checking for air in the fuel system and vacuum might help find something

[pstephens46]

Try running the motors on a portable tank of fuel. That may help to isolate fuel or tank issues.

[Nicturner808]

The light on the gauge is not a WIF it is an engine icon,but I think it just hit 100hrs so might be a maintenance light? Will try to run in different tank and seewhat happens.

[TownsendsFJR1300]

At the bottom of the VST should be a phillips head screw and a clear hose attached to the tank.

Loosen the screw, (which drains the VST), and catch in a container for examination, part #13:
http://www.boats.net/parts/search/Ya...201/parts.html

Any water in the system will be quickly visible...


You should also have an under cowl fuel filter(clear plastic container). It has two wires attached to it.
Check those for water as well:
http://www.boats.net/parts/search/Ya...UEL/parts.html


.

[pstephens46]

How does Yamaha decide which engine model gets a water in fuel alarm?

Wouldn't it make sense to have it on most every engine?

I feel cheated and inadequate.....

[99yam40]

apparently that is the way they felt too.
why does it only alarm in neutral

[TownsendsFJR1300]

How does Yamaha decide which engine model gets a water in fuel alarm?

Wouldn't it make sense to have it on most every engine?

I feel cheated and inadequate.....

inadequate, perhaps....

Don't feel cheated.

In ours, (F150), that cup is about $8.00, the slightly newer cups, with the sensor, $127.00 , part #8:, http://www.boats.net/parts/search/Ya...201/parts.html

I rather look back at my fuel / water separator.

One less thing to break..

And I believe it's only in the newer models...

[rodbolt17]

define newer????
most all four strokes above about 40 HP have had water detect since about 07.
that 10 yr old motor is about an antique.

[TownsendsFJR1300]

define newer????
most all four strokes above about 40 HP have had water detect since about 07.
that 10 yr old motor is about an antique.

Newer as in NEWER THAN 2006. Just like Petersons, mine and as I re-call, your F150

So it's 11 years old? So are at least half the engines on this forum. Point being?