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I have a 2003 200 hp. Yamaha 2 stroke EFI. It only has 87 hours on the engine, and it already has carbon build up on the 02 sensor. I run ring free. I used to run a 15:1 ring free ratio until this bulletin board suggested I switch to a 10:1 ring free ratio. I now use the 10:1 ratio.
What else can I do to stop the carbon build up?
Miami Vice
1999 23 Regulator-2 2003 Yamaha 200 HP HPDI's. President Onslow Bay SW Fishing Club, Chair of Onslow Bay Open KMT, 100% volunteer, benefits underpriviliged Kids in Eastern NC. $12,000 raised for Eckerds Camp E Ma Henwu 2002 Tourn., $6800 for Take A Kid Fishing 2001 Tourn.
The battery is not the cause of any problems on the EFI's, it may cause problems with the larger HPDI's.
I assume you have pulled the O2 sensor and seen some carbon?? My first question would be on oil consumption. What ratio of oil to gas are you burning. It should be somewhere in the neighborhood of 45:1. If it is lower, you probably need to have your oil linkage adjusted. Over oiling will cause buildup on the O2 sensor. I also would recommend periodic decarbonizing. I do my twin 250's every 50-75 hours and in 700 hours have had zero O2 problems. Here is a link that someone posted a while back that gives you everything you need to know about the O2 sensor. The main points are use a good quality oil, decarbizing, proper linkage adjustments and using ring free.
CADD, it is pretty rare since the 2000 model EFI's to have an O2 problem but the most common symptom is surging rpm's. The above article outlines other symptoms.
Not only the oil link adjustment, but the TPS could be out of adjustment, causing it to run rich. Engine temp sensor can also make the engine run rich.
It is normal to have some carbon on the 02 sensor.
I just checked the sensors on my 250 OX66's last week at 310 hrs. No carbon to speak of on either one, both were a light tan color. I've never used a drop of Ringfree, but I do use Ficht Ram Oil exclusively.
Kirk@reel_time
I believe the oil injection extremes are 50:1 at WOT and 100:1 at idle. Any time your overall utilization is less than 50:1, you are over-oiling. I know mine runs about 65:1.
Silicon spray-oil on the engine
It is my understanding that the only spray oil that will not contaminate the O2 sensor is the Boeshield T-9. However, the contamination does NOT come from spraying the external O2 sensor component. It comes from the vaporization of the oil on the engine surfaces at normal engine running temperatures. The vaporized oil is sucked into the air intakes and contaminates the O2. Even the Yamaha Silicon spray is a no-no.
Gil, I average right around 45:1, I disagree that is over oiling. Certainly the rule of thumb is 50:1 but almost everyone I know running 250 OX66's is running between 40-50:1. The exact amount I burn is very dependent on throttle position. If I push the boat hard (i.e. +4700 rpm's) I get low 40's:1, if I take it easy I get closer to 50:1. I am positive my oil linkage is adjusted correctly as I have a top notch Yammy certified mechanic. I bet if you conducted a poll you would find very very few averaging more than 50:1. AT 65:1 I would be concerned about not enough oil.
Kirk, you may be correct. Better to err on the side of over-oil rather than under-oil. The 50:1 and 100:1 figures are from Yamaha and obviously everyone must go through idle at some time. Consequently, you would always expect an average above 50. I do a lot of low speed trolling and on my 2 recent off-shore trips my overall average speed was slightly less than 10 MPH for each trip (per Garmin 2006). I estimate that only 20% of my trip time is at RPM's between 3500 and WOT. Without fine tuning the math, the 65:1 seems about right for me.
If I were averaging 45:1 and the engines were happy, so be it.
The batteries have to meet certain specs according to Yamaha for the OX 66s.
The OX Sensor has not been a problem on the HPDI's. I am on my 3rd set of 200s and getting set #4, no Ox Sensor problems.
1999 23 Regulator-2 2003 Yamaha 200 HP HPDI's. President Onslow Bay SW Fishing Club, Chair of Onslow Bay Open KMT, 100% volunteer, benefits underpriviliged Kids in Eastern NC. $12,000 raised for Eckerds Camp E Ma Henwu 2002 Tourn., $6800 for Take A Kid Fishing 2001 Tourn.
Stan, I did not mean there are no minimium requirements for batteries on the OX66 just that the OX66 are not nearly as sensitive to batteries as are the HPDI.
Don't understand why battery specs have a direct relationship to the O2 sensor. The O2 sensor has a heater circuit that only preheats the elements when cold after that the combustion chamber temperatures of more than 600 deg F keep the sensor hot enough to function properly. O2 sensors in their startup mode don't require that much current to where it will tax the batteries. So I really don't understand why a battery spec makes a difference, unless of course there is so much draw from other devices that the alternator and batteries can't keep up with it. Other than that, if the batteries and alternators provide enough juice to power everything, can't see why it's so critical!
Carbon build up on Yamaha 02 sensor 
