O2 sensor location?

[Kiddcloud]

I've been experiencing issues with engine cutting off on me at idle after cruising. I'm leaning toward the o2 sensor as the suspect. Plugs were real wet and black.

The problem now is trying to locate it.

I have a new to me 1997 Yamaha ox66 EFI 250 HP

Where is it located?

[boats.net]

That is not a fuel injected engine, it's a carb model. Need to get correct service manual for that model number motor.

[Kiddcloud]

Ok. The engine cowling said EFI, but I guess that was a replacement at some point from the previous owner.

Since it is a carb model, does it even have a o2 sensor? If not, what do you advise me to check or replace? Where can I get a digital or paper copy of the service manual?

Would fuel treatment or cleaner such as SeaFoam help my issue?

Thank you very much.

[99yam40]

local Yamaha dealer can get you a service manual or you can order directly from Yamaha.

Pull and clean carbs and then follow procedures in manual for link and sync. It will have all specs

[jb123]

Do yourself a favor and shrinkwrap those crimped connections on starboard side if you expect
Them to last

[rodbolt17]

no O2 sensor on that engine.
however that engine was hard on fuel pumps.
if the enrichment injector orings leak it floods.
that range we also had some stator issues.
as the stator got hot,especially at low speeds, the input voltage to the CDI, and CDI output, would fall.
less than about 60V peak and it quits.

[Kiddcloud]

no O2 sensor on that engine.
however that engine was hard on fuel pumps.
if the enrichment injector orings leak it floods.
that range we also had some stator issues.
as the stator got hot,especially at low speeds, the input voltage to the CDI, and CDI output, would fall.
less than about 60V peak and it quits.

Thank you for answering the o2 sensor question.

The previous owner of the boat showed be a trick to start the engine when is cuts out like that. He told me to tilt engine all the way up, wait 1 min, and try to restart with the engine still tilted.

It works, but it such a hassle and it happens at the darnest time (last time in the channel, blocking boating traffic).

Would it be safe to say that the carbs are getting flooded causing the idle cut offs? Would cleaning the carbs resolve that?

[rodbolt17]

you really really may wish to use the yamaha marine dealer locator function and find a technician near you with a master tech certificate.
the last of the carbed 3.1L motors was about 1996 and a lot of the techs that knew them are long gone.
the Tstats have to be in working order or it causes issues.
the orings for the enrichment solinoids must seal.
the orings for the soliniods are NOT part of the carb kit and are ordered seperatly.

this engine was hard on lift pumps, test them carefully.
I ususally replace them every 3rd season.

this engine can be tested for codes with the diagnostic test lamp.

by trimming it up your forcing it lean.
your also most likly starting it with the water pump intakes out of the water, begging for a total and catastrophic pump failure.

[Kiddcloud]

you really really may wish to use the yamaha marine dealer locator function and find a technician near you with a master tech certificate.
the last of the carbed 3.1L motors was about 1996 and a lot of the techs that knew them are long gone.
the Tstats have to be in working order or it causes issues.
the orings for the enrichment solinoids must seal.
the orings for the soliniods are NOT part of the carb kit and are ordered seperatly.

this engine was hard on lift pumps, test them carefully.
I ususally replace them every 3rd season.

this engine can be tested for codes with the diagnostic test lamp.

by trimming it up your forcing it lean.
your also most likly starting it with the water pump intakes out of the water, begging for a total and catastrophic pump failure.

Thank you.....