Question on OX66

[Freezebear]

My neighbor just bought a used boat with a newer OX66 Yamaha 225HP. He had a mechanic check it out and said it all looked good and everything is still original. My neighbor says it runs a little rough at lower RPM's but runs smooth at higher RPM's. The mechanic told him that the reason for this is that at lower RPM's it cuts out 2 cylinders for improved fuel economy. Is this true or is the mechanic handing him a line of crap? If so what can we check on it? Also what is recommended full speed RPM's for this motor?

 

[John from Madison CT]

Re: Question on OX66

Yes, it's true, they are not great idlers, but rest assured that this is OK.

 

[bigbrownbuku]

Re: Question on OX66

on the hose they run fairly rough, in the water its much harder to notice.<br />if the service history is sketchy direct him to this website and do a quick search on ox66 problems and solutions.

 

[fondafj]

Re: Question on OX66

Freeze,<br /> Read on in these forums --- there is a BIG difference between a mechanic and a knowledgable Yamaha mechanic. I too though my '99 OX66's idled a little rough and after replacing my O2 sensors, they now idle smooth as silk----comparitively speaking.

 

[Freezebear]

Re: Question on OX66

Thanks everyone. That is strange that these motors have O2 sensors in them. In cars, O2 sensors are fouled easily by rich mixtures and oil. Seems these would not last very long in a 2stroke. This motor has sat a long time before he bought it. I will go out with him soon and see how bad it runs. Thanks for the info.

 

[rodbolt]

Re: Question on OX66

they do go bad often. thats why cleaning every 200 hours OR annually is mandatory. if you suspect its bad test it with the proper test harness and DVM before operation. if it leans out it takes #1 piston with it. i dont design them i just fix them. if you dont believe then be prepared to replace the o2 sensor at rebuild. if it sat that long then fuel pumps and vapor seperator cleaning and VST filter service is a must. a water pump wont hurt.the 3.1 L motors are hard on fuel pumps when all is well. lean out the fuel mix with bad low pressure pumps or clogged VST filter or a incorrect reading O2 sensor and you will get to see the internals on the engine soon.

 

[edeuka]

Re: Question on OX66

how do you clean o2 senser must you remove it or will sea foam or other decarb clean this

 

[fondafj]

Re: Question on OX66

edeuka,<br /> Do a search and you will find a ton of info on cleaning the O2 sensors. They must be removed and the mounting block should be removed and cleaned as well. <br />Here is some good reading describing the basic concepts and cleaning.<br /> http://www.boatsetup.com/O2sensor.pdf