1999 Yamaha OX66 loosing power

[Fishin Technician]

Rodbolt,
I have had this motor for 2 years now. I bought it slightly used, but was able to get a YES warranty on it which is good until May/09. In Sept. it started acting funny ( once in a while )where I would have to give it more throttle to stay on plane than usual and I also noticed fuel burn would go WAY high sometimes reaching 30GPH. Also it would loose RPMs at the high end by about 500. Last spring I had replaced the VST/Lift pumps,filters,hoses (no problem, just PM)and it ran fine from June-August. A budy of mine with a 250 had a very similar problem this year and had the O2 sensor replaced to fix it. So, I talked to a local mechanic and he didn't seem too interested in looking at it because it was intermittant and he was busy winterizing. He said check the bottom of the boat for growth and check the plugs, check the prop which I did and found no problems. Now the boat is on the trailer and I am wondering if I should winterize or take it in to see if he can do anything or check some things myself so that I won't loose time out of the water in the Spring.
What would you do? Thanks/Frank

 

[rodbolt]

Re: 1999 Yamaha OX66 loosing power

its trying to tell you its sick. listen or it may get sick and die.
O2 sensor maint is just that. maintenance.
VST filter cleaning is maint as well.
also check the plug caps. its quick and simple.
if kept maintained,means fix it before it breaks, that motor will go thousands of hours.
dont rely on a tech to tell you what to do as to many techs wont or dont.

 

[bernieb]

Re: 1999 Yamaha OX66 loosing power

Not a rodbolt superman here, but your symptoms were similar to my 250 ox and a good spraying in the plug holes with a de-carb and running a can of seafoam in a six gallon auxillary tank created a hell've lot of smoke and then it ran like a scared rabbit. Have you been using wallmart oil? if so get started.

 

[ronzoe]

Re: 1999 Yamaha OX66 loosing power

I've got twin 1998 EFI's that had similar problems, went the whole gamut with O2 sensors, lift pumps, plugs etc..with little success. Finally went to a Yamaha dealer, purchased some "ring free" and ran it through the engines in the "shock" mode as described on the bottle. Used an old 6 gallon tank to do this on each engine. I think you will find that may be your solution. "Ring free" is similar to the "Sea Foam" mentioned in a prior post. The irony is the last thing that I did was the least expensive. Wish I had done things in the reverse order. Good Luck. Ronzoe

 

[Fishin Technician]

Re: 1999 Yamaha OX66 loosing power

Thanks for the replys.

Rodbolt, forgot to mention but I had removed and cleaned the O2 sensor this spring as well as replaced the plug caps ( I had a couple caps with rust, so I replaced them all ). I will pull the O2 sensor VST and check them out, but they were actually clean when I did them in the Spring. I have been doing maintenance according to the yamaha reccomendations. It is more convienient and I like working on the motor myself rather than brining it in all the time. Also, I run ringfree in the normal reccomended amount and I use yamalube. I bought the YES as an insurance policy because the motor had been used, but it sounds like itis useless in this situation.

Sounds like Bernieb and Ronzoe had some luck with seafoam, so I willgive that a try. Do you think the seafoam cured it because it cleaned the O2 sensor or some other reason?

Problem now is that the cold has set in, so that will slow me down a bit.