Assuming yours is a 1999 OX66 250 like mine (SX250TXRX)...
Yes
Also, you don't mention what the engine is doing at idle. Is it idling smoothly (relatively) at 750 or so RPM, or is it idling at 1100 or at 500? If idling at 1100 you have some kind of sensor fault, which throws the stupid ECU into "panic" mode, locking the timing and max throttle. If idling too low, you probably have a TPS problem.
Idle is good
How is the compression?
100PSI all around
Have you done a spark test?
Not sure if you mean did I pull and check for spark. No - not sure what a spark test is other than what I'd do on a lawn mower engine.
Have you done a fuel pressure test? (I'd start there). Really easy to do if you have the pressure gauge - simple Schrader valve on the fuel rail.
Got the tool but have not done yet.
Depending on the maintenance history, I'd replace all the fuel components if you either have not done so, or are unsure of the history. This will give you a baseline.
1. Replace LP fuel pumps. Save the old ones - you can rebuild them in the winter and have them as backups.
https://www.simyamaha.com/ProductDetail ... 0-03-00KIT
2. Replace VST filter, and clean VST tank. Pay attention - is there any goo in there?
https://www.simyamaha.com/ProductDetail ... 3915-00-00
3. Replace on-board fuel filter. Cut up the old one - how did it look?
https://www.simyamaha.com/ProductDetail ... 3-00-00SET
4. Replace water separator/fuel filter - cut open the old one, how did it look?
http://www.simyamaha.com/Racor_Fuel_Fil ... 220sul.htm
Get a gasket set for the O2 sensor:
https://www.simyamaha.com/ProductDetail ... 1135-00-00
Pull the O2 sensor and inspect it. More importantly, pull the "dip tube" (it will be a round "knob" sticking into the O2 sensor body; once you remove the sensor body, it will be sticking up out of the engine block). Soak the dip tube over night in Deep Creep. I think cleaning the O2 sensor is dangerous; my opinion is that if you clean this (and do all this other stuff) and it still doesn't run right, test the O2 sensor
Yep that will be next, will probably do anyway just for fuel efficiency.
Pull all the spark plugs, flush each cylinder liberally with Deep Creep and then "bump" the starter to swish the stuff around in there. Let sit overnight
Actually had just done that prior to the test run. Wow what a cloud of smoke across the harbor. No breeze made it look erie & nasty. Sort pissed off some tourists sitting on the deck of their high priced rentals. They had to go in side to get away from the smoke.
Install new plugs. When you do this, check the caps for resistance.
Hmm - have never done that.
Test the High Pressure Resistor per the manual. If out of spec, replace.
I'll have to look that one up in the manual.
Now fire the motor up (it will smoke like Hell because of the Deep Creep). Test the O2 voltage output (you can back-probe the connections, but it is much easier with a test harness). if your seeing .1V or .9V in the water after its warmed up you have serious sensor issues. Warm idle should see something in the order of .35-.65 and flucuating, at 3000-4000 RPM it should stay between .3 and .45 V. If out of spec and you have cleaned the dip tube, replace the O2 sensor. Bad O2 sensor will cause the motor to lean out over 3,000 RPMs (IIRC) and obviously dangerous. According to some techs I've talked to, this is the most common cause of engine failure on the Ox66
If the O2 sensor readings look good, congratulations you just saved $200.
If the idle is in spec (around 750 RPM) and everything else checks out so far, but you still have performance problems it is time to start running checks on the spark and ignition system (this might also be a good place to start).
I'm not a professional mechanic, so I may be totally wrong on some of my suggestions, but this comes from my experience wrenching on my own Ox66 motor.
Yup - thanks for that. Done some my self, but yours seems more exhaustive.
Get a "Winky blinky" so you can see if the motor is throwing trouble codes. Call your local Yammie mechanic - they may loan it to you so you can hook it up and run the boat on the water for a while and track all the codes. None are stored - you have to catch it in 'real time" while the motor is complaining. You count the flashes. For example it will go: "flash, flash, flash, flash...............................flash" That is a "41" code (over rev limiter kicking in). The table for interpreting codes can be found in the manual. It will flash a "31" (IIRC) at first then switch to flashing "1" constantly when it warms up.
I have one, but have not plugged it in. The bugger has a lot of different connectors. Not sure which of the 3 get connected. I assume i should just connect the larger ones and match the wires on the blinky to the wires on the motor. Not sure what the dangling wire w/ the plug is for. No good reference for how to connect on line.
The hardest part is getting all the little problems fixed and doing it in the right sequence.
Personally, I hate this engine because it is so simple, yet so bedeviling to get set up correctly if you don't start in exactly the right place and follow exactly the right procedures. It reminds me of trying to romance a high maintenance woman - if you mess it up along the way, she slaps you in the face, walks away, and you have to start ALL over again, spending more time, energy, and angst in the process...
You forgot and takes your money!
Hope that helps....
Yep - thanks. As always I will report back my misfortunes & successes. Gawd I love the "internets" for this stuffHere's another thread I started on this motor a while back:
What I've Learned about the OX66 Motor
