225 ox66 question / advice

[miky2884]

Questions about my motor, few things that are going on that im pretty sure aren't normal.
First thing, i have noticed over the past month on the initial cold start up the motor usto start around 12-15 RPM's until it warmed up now as soon as it fires it idles around 600, if I recall a past thread here I believe someone said the motor should start at a higher RPM.

Second i am only getting around 5100 RPM's out of it at WOT, and i noticed last night there is no fluctuation in RPM's however I can hear the motor missing. Basically just seems that the motor is running rough, it doesn't stall idels fine etc....

I haven't really done anything to this motor since buying the boat, Only thing I have done is change the spark plugs. Any recommendations would be appreciated.

 

[Megabyte]

That motor maxes out at 5500, so 5100 isn't bad. You could under-prop her a little more and get more RPM's... but why?
FWIW - My OX66 runs 5100 at WOT and I'm fine with that. 34 kts on flat water with 2 aboard, full fuel, and all my gear.

These motors are pretty simple. So long as the fuel filters are clean and the O2 sensor is clean, they will run forever.
Do you add anything to the fuel when you fill up? Ringfree? StarTron? StaBil? Something else?

 

[Brent]

How many hours on the plugs? Maybe needs to be cleaned and re-gapped or replaced?
O2 sensor been cleaned?
You can use an portable gas tank and add Seafoam at cleaning ratio to clean out the fuel system.
I would serach on OX and OX66
There are a lot of tips
Maybe you can summarized them for everyone!

 

[miky2884]

Kevin thanks for the response, i have to admit I don't run anything in the fuel i keep the boat with no more then a half tank of gas and i use it 2-3 times a week, i know still no excuse and starting today i will start running ring free through it.

I have been reading a lot of stuff this morning i believe my problem is either a dirty o2 sensor or the VST filters. i am gonna try and clean the o2 sensor first and change the regular fuel filter. Like I said the motor isn't running terrible just seems to be missing a little at higher RPM's.

 

[miky2884]

How many hours on the plugs? Maybe needs to be cleaned and re-gapped or replaced?
O2 sensor been cleaned?
You can use an portable gas tank and add Seafoam at cleaning ratio to clean out the fuel system.
I would serach on OX and OX66
There are a lot of tips
Maybe you can summarized them for everyone!

Brent,
Plugs are new as of about 2 months ago
I am going to do the seafoam treatment
I haven't done anything to this motor since i bought the boat over the winter, i kinda went on the fact if it isn't broke don't fix it, but now its time i have to spend some time to do these things

 

[Brent]

good luck

Good point about the VST filter

In addition to Ring Free, Yamaha has
Yamahalube Fuel Stabalizer & Conditioner PLUS
see http://www.simyamaha.com/category_s/1725.htm

Looks like you can add both to the gas.

 

[dadsdayoff2]

I have owned the same motor for 6 seasons and have had a few small issues that can be fixed by yourself. First of all, I only get around 5100rpm wot like Capt.Kevin. When my O2 sensor was dirty/bad, my fuel consumption was higher & my WOT was reduced greatly and fluctuated. I replaced the O2 sensor and started running ring free, no problems since. I have changed/cleaned my vst several times. I now change/clean it at the beginning of the season. EVERYTIME my vst was dirty, the motor would buck and jive starving for fuel. Good luck and please advise us if you figure it out.

 

[Brent]

Here is article on O2 sensor service
http://www.boatsetup.com/O2sensor.pdf

 

[dadsdayoff2]

Here is article on O2 sensor service
http://www.boatsetup.com/O2sensor.pdf

Great read and a must read for anyone with a OX66 motor. Thanks for sharing!

 

[miky2884]

Thanks guys i plan on cleaning the o2 sensor and change the VST filter this week. Deom what I have read it seems thats where my problem is. Ran the boat all weekend and it ran fine just a few hesitations. I will post and let you know how i made out

 

[Brent]

decarb thread using external fuel tank

viewtopic.php?f=19&t=10155&p=71275&hilit=seafoam#p71275

 

[Brent]

another O2 sensor article thanks to Andy at Sim

http://www.simyamaha.com/category_s/1841.htm

 

[Megabyte]

Keeping the O2 sensor clean is one of the reasons I use Ringfree, StarTron, and StaBil at every fill-up.
1 ounce of each, per every 10 gallons of gas is the 'maintenance' dose.

 

[gw204]

If you don't know the service history of the engine, I would...

-check/clean the O2 sensor and draw tube
-replace the spark plugs
-change the engine mounted fuel filter
-clean/replace the VST filter and clean the VST tank
-set the oil pump linkage
-snyc and link the throttle bodies
-adjust the TPS
-change the lower unit oil
-replace the low pressure fuel pumps

Andy @ Shipyard Island can get you all the procedures for doing so. Just make sure you buy your parts and supplies from him (not that you'll get better service or prices anywhere else...).

 

[Megabyte]

+1

forgot to mention the low pressure fuel pumps.
They should be replaced about every 3 years or so.

 

[Phil]

My 1999 ox66 was also missing at higher rpms and it turn out to be one of the spark plug wire/coil pack. You can check them by removing each wire and measuring the resitance. All 5 other wires had the same resistance except one, replaced the bad one and the engine felt like new again.

 

[SBH2OMan]

FWIW, my Ox66 will run 5700 before the rev limiter kicks in (according to the winky blinky). Yea, I know I'm under-propped.

These motors are simple, but just complex enough to be a real PITA to get dialed in when they are having troubles because they don't tell you much. I think you are on the right track. Go through the fuel systems first and see if that cleans things up, then look at the O2 sensor (there is a Bosch replacement for $50 that you can splice the wires onto and save $250).

You can check the low pressure fuel pumps by priming the bulb and seeing if they leak. They are about $50 to replace. When they are bad it will usually cause a slightly different symptom - inability to get to WOT at all and there will be a sharp stumble and drop-off of RPMs when you try. Then when you ease off the throttle, the rpms will pick back up again. Doesn't sound like your problem.

Check your VST filter for gunk. If dirty, replace it along with the paper fuel filter that is on the engine.

Visually check the O2 sensor and dip tube and make sure they are clean. If they are, use a test harness to test the voltage output WHILE UNDERWAY (testing at the dock or on ear muffs will be inconclusive - ask me how I know...)

For de-carb I recommend the following procedure which I find easier than using a separate tank:

Pull the spark plugs for inspection/cleaning/replacement

Pull the airbox (be careful of the two little rubber hoses)

Spray Deep Creep into all the plug holes and into the throttles

Bump the starter to "swish" it all around inside.

Let sit overnight and fire it up the next morning. Be sure to be upwind, and make sure you don't have anyone you care about downwind - it will smoke like a forest fire for a minute or so.

Also, everything you do, make sure you test it with the cover INSTALLED before you call it good. I have had several situations where she ran GREAT until the cowl was installed, then would not run. Still a mystery to me, but I blame it on some wiring.

 

[Brent]

I am learning a lot from these postings.

How often do you change the thermostat?

How is it replaced?

 

[Megabyte]

How often do you change the thermostat(s)?

Every 3 years, along with the poppit valve.

 

[SBH2OMan]

At the risk of turning this into an Ox66 "ubër-thread", I'll add that with an older motor like this, its a very good idea to change the ENTIRE water pump assembly instead of just the impeller. SIM sells a complete kit. I replaced mine recently and luckily, I had the entire kit because the plastic housing was in really bad shape from so many years of POs just changing out the impeller.