New to me OX66 225

[Grady_Crazy]

I have a new to me 2000 Tournament 225 with a 2000 225 ox66. This is a good engine and my wife says for a 2 stroke this is her favorite. I do have a question about performance.

I know it drops cylinders at low speeds but is this normal. From 800 to 1400 rpm runs a little rough but ok. From 1400 to 1900 shakes some what making me think something is wrong. At 2000 rpm it shoots up to 2600 and really moves. Is this normal or is something amiss?

The vst filter has been cleaned, fuel filter and the 3 low pressure pumps replaced, new spark plus and the oxygen sensor cleaned. It starts immediately and the bulb Pumps up good and hard. Not so before the lp pumps replaced. WOT is 5300 with 1 person, me.

 

[family affair]

I too have wondered how "normal" rough running is with the ox66 below roughly 2000 rpm's. My experience has shown this engine to be a fickle beast at idle to about 2k. Things that seem to affect it most are fuel quality and type, along with temp, humidity, and throttle position sensor adjustment. Our 225 seems to run better in the low range with winter blend fuel, although economy suffers. I don't know if ethanol has any affect because e10 is what we mostly use. Any marine gas we have ran has given terrible results including rougher running and missing.

The tps is extremely touchy. You can actually get the numbers to fluctuate out of spec by lightly twisting the sensor when it is securely fastened. The tps seems to have the greatest impact on low end running. It needs to be adjusted while in the water because exhaust back pressure impacts the reading.

Clean injectors can have an impact too.

I'd be curious to know if anyone has gotten an OX66 225 to consistently run smoothly. Every one I have ever observed runs as good or worse than ours on the low end. Our 5 star Yamaha mechanic didn't think our results were unusual.

If you are consistently experiencing rough running and you are confident fuel is not to blame, I would check the tps readings and see if it is within spec.

Please let us know how it goes.

 

[Grady_Crazy]

The fuel is all fresh. I had all the gas in tank pumped pumped out by the prior owner. I then had new marine fuel added, non ethanol. I was told these engines don't like to go slow.

 

[Parthery]

Grady_Crazy, you need to update that signature :grin:

My 225 is only fickle on cold starts....it doesn't always want to kick in the fast idle mode so it tries to idle at 7-800 RPM while cold which makes it rather lumpy....it doesn't stall out...it's just not smooth. Once it's warm it starts with a flick of the key and goes up to about 900 or so before it settles down.

Mine is smooth from 2000 on up...at times I'll get a bit of a surge between 4000-4300 but then it smooths right out and pulls strong all the way to 5500. The fact that it doesn't do it all the time leads me to believe that it might just be that that VST could use a cleaning....which I will do at the end of the season. It's barely noticeable and you really have to listen for it or watch the tach.

I'm burning - for the most part - E-10 and using Ring Free and Sta Bil....I'm going to switch back to PRI-G though as it's now available through Amazon and I've had good luck with it. All of my hoses have been replaced with Ethanol resistant so I'm comfortable using E-10.

 

[seasick]

Grady_Crazy, you need to update that signature :grin:

My 225 is only fickle on cold starts....it doesn't always want to kick in the fast idle mode so it tries to idle at 7-800 RPM while cold which makes it rather lumpy....it doesn't stall out...it's just not smooth. Once it's warm it starts with a flick of the key and goes up to about 900 or so before it settles down.

Mine is smooth from 2000 on up...at times I'll get a bit of a surge between 4000-4300 but then it smooths right out and pulls strong all the way to 5500. The fact that it doesn't do it all the time leads me to believe that it might just be that that VST could use a cleaning....which I will do at the end of the season. It's barely noticeable and you really have to listen for it or watch the tach.

I'm burning - for the most part - E-10 and using Ring Free and Sta Bil....I'm going to switch back to PRI-G though as it's now available through Amazon and I've had good luck with it. All of my hoses have been replaced with Ethanol resistant so I'm comfortable using E-10.

If your motor "pulls strong all the way to 5500" the VST is not clogged. The surge could be a lot of things, TPS as mentioned or throttle body sync. It could be something as simple as a bad helm control or worn control cable too. Then of course there are possible spark issues too. Bad/dirty injectors can cause issues when they don't shut off as quickly as called for. That causes a too rich mixture. At higher speeds, a slow to close injector is not as much an issue as it is at lower revs since more fuel is needed.
Not fast idling when cold is a different issue but could be related. Your rough idle when cold is due to the fact that the ECU apparently doesn't know the motor is cold. That could be caused by a bad temperature sensor. Testing of the sensor is relatively easy. Note that if my memory serves me correctly, there is one temp sensor and two thermal switches. The temp sensor is pressed into a grommet on one of the heads. It's resistance changes as a function of temperature. It can be tested with an ohmmeter and a pot of water on the stove.

 

[seasick]

I have a new to me 2000 Tournament 225 with a 2000 225 ox66. This is a good engine and my wife says for a 2 stroke this is her favorite. I do have a question about performance.

I know it drops cylinders at low speeds but is this normal. From 800 to 1400 rpm runs a little rough but ok. From 1400 to 1900 shakes some what making me think something is wrong. At 2000 rpm it shoots up to 2600 and really moves. Is this normal or is something amiss?

The vst filter has been cleaned, fuel filter and the 3 low pressure pumps replaced, new spark plus and the oxygen sensor cleaned. It starts immediately and the bulb Pumps up good and hard. Not so before the lp pumps replaced. WOT is 5300 with 1 person, me.

The disabled cylinders will cut in usually by about 1100 rpm. The motor should still run smoothly though.
The shaking at mid range can be many things. Do you see the motor shaking or do you feel it in your feet? If the later, the shaking may be a prop issue. Unbalanced props shake but the vibration can reduces as speed increases.
In general as I mentioned, mid range issues where high end performance are often due to fuel issues, something as simple as one sticking/ dirty injector. It is difficult to identify dirty injectors, especially if one is acting up. If all other systems check out, it might be time to have the injectors cleaned and documented.
I also mentioned that the throttle bodies may have to be synced. They don't get out of sync often but they need to be checked now and then.
One simple method ( not the most accurate but close enough as a good starting point) is to disconnect the throttle cable at the motor, back off the main idle screw ( count how many turns you take out), verify that the other 5 throttle sadjusters are touching their stops. If not adjust as needed.
Turn the main idle screw back in ( the turns you counted), reconnect the throttle control cable, make sure it is adjusted correctly for neutral and idle) start the motor, let it warm up, adjust the idle screw to spec ( 730 revs or so, I am not 100% sure) and see if there is a difference in performance.

 

[family affair]

I would need to double check my service manual, but I'm reasonably sure 225 ox66 changes the number of firing cylinders twice between idle and 2200 rpm's. At 1100 not all 6 fire.
Our engine consistently ran as yours did before doing all the same maintenance. The engine ran rough enough to vibrate the windshield and bow rail. The tps adjustment seemed to have the greatest impact. Injector cleaning helped too.
2 other things to mention:
- Despite everyone swearing how great it was, Valve tech marine gas caused stalling and very rough running. I'm sure that doesn't happen everywhere, but you might want to try running off a tank of fuel you have 100% confidence in.
- Our engine runs smoothly most of the time, but I have observed the following: idle to 1200 rpm can still be a little rough when cold. I suspect the engine runs off computer fuel and ignition maps until the O2 sensor heats up. If the engine runs a little rough at this range, I don't touch the throttle and within a few minutes it will run smoothly. My guess is the computer starts taking data off sensors to make adjustments. Seasick might know for sure.

Ultimately a competent Yamaha mechanic giving it a once over and answering my questions helped me to have confidence in what was typical and what should require attention. From what you describe, I would find a 5 star Yamaha guy and let him have at it. A few hundred $$ well spent IMO.

 

[seasick]

I would need to double check my service manual, but I'm reasonably sure 225 ox66 changes the number of firing cylinders twice between idle and 2200 rpm's. At 1100 not all 6 fire.
Our engine consistently ran as yours did before doing all the same maintenance. The engine ran rough enough to vibrate the windshield and bow rail. The tps adjustment seemed to have the greatest impact. Injector cleaning helped too.
2 other things to mention:
- Despite everyone swearing how great it was, Valve tech marine gas caused stalling and very rough running. I'm sure that doesn't happen everywhere, but you might want to try running off a tank of fuel you have 100% confidence in.
- Our engine runs smoothly most of the time, but I have observed the following: idle to 1200 rpm can still be a little rough when cold. I suspect the engine runs off computer fuel and ignition maps until the O2 sensor heats up. If the engine runs a little rough at this range, I don't touch the throttle and within a few minutes it will run smoothly. My guess is the computer starts taking data off sensors to make adjustments. Seasick might know for sure.

Ultimately a competent Yamaha mechanic giving it a once over and answering my questions helped me to have confidence in what was typical and what should require attention. From what you describe, I would find a 5 star Yamaha guy and let him have at it. A few hundred $$ well spent IMO.

Thanks for implying that I might understand how the SXs work but I am as mystified as most everyone else. Wouldn't it be nice for someone to publish a really detailed document on what goes on in a specific marine engines?
You might be right regarding the rpms for all cylinders on the 250. I was basing my number on the SX150 specs.
Regarding ValveTech, I use it and haven't had issues but I am very cautious in the beginning of the season where I get fuel. Often, the fuel docks in my area sell very little gas during the winter and therefore the gas sits in their tanks. When the boating season starts, the first ones to gas up get the old fuel and whatever accumulated during the off season. Sometimes you have no choice but if you do, I like to wait until I know the fuel dock has a new load.

You are also spot on about the O2 sensor in that it doesn't work correctly until it is hot. Assuming is is not an open circuit, it will call for a rich mixture when cold and that is fine for starting. Rough operation for a few minutes is typical for SX motors. In many cases, the motor will need to be run under load a bit to make the roughness go away. I am not sure why that is but it may just be the need to unfoul the plugs that were run rich at cold start or perhaps things just need to get warmed up.

 

[Grady_Crazy]

I do like the engine, funny low speed or not. It starts immediately and has plenty of power. Not nearly as loud as a 200 HPDI which I have had in the past. At cruise no difference in the OX66, HPDI, or 4 stroke.

What I also like is that I have a 22 ft Grady White in good shape for a mere fraction of what a new Tournament costs. It also does not have all the plush features like upholstery one has to maintain. Rides comfortably, fast, plenty of room and fishable. When I take it trolling I will see how the low speed issues suit me.

 

[Grouper Duper]

Back when we had our Seafarer with that engine, we experienced similar behavior. We ALWAYS had significant improvement after performing a "decarb" with Seafoam. Once or twice a year worked for us; it's cheap and easy to try.

 

[GreatWhite23]

Ring free makes a difference in my 250 ox66. . I like the motors just fine. It is a two stroke just saying.