ghind O2 ?

What does your O2 sensor read for voltage at idle. Mine reads like your default map info in O2 sensor post. But if it is doing this its not the O2 sensor so what is it?

You mean why is your engine running rich at idle??

How is it running at other RPM (voltages and explanations of their speed and range of movement please)

If you had blown low pressure pumps, it would run rich.

Also a battery that is a bit low or electrical draw which is too high will do it. Happy to help but need lots more info.

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Yes it runs rich at idle as in above 750mV at idle. The reason I am looking at this is the powerhead was just rebuilt by the experts at HYDRO TEC low pressure pumps were rebuilt injectors cleaned and all fuel screens and filters changed. So its just coming off the double oil break in. It doesnt reach the rpm that it should its off by about 500. I know from the past that when its down to 5200 O2 sensor can have a problem. I have two ways to test this battery and both show its OK. The only way I can see a battery causing this is if it effects the heater part of the of the O2 or very low battery voltage causing ECU to run a rich mixture and I know thats not an issue because the O2 is over the crossover voltage in less that a minute of running and it starts fine. What I saw the other day was at idle it read 750 to 780 mV at idle. At 2500 to 3000 it varys 250 to 450 mV and is around 650mV at WOT 5200 RPM. Using the same prop that has always been on it. I really think its OK just wanted to get your ideas after I read the post at the top of the page. Shouldnt it vary some at idle and run higher at WOT. I also know that when it was new dealer told me that due to the double oil break in it would foul the O2 sensor.I will try new plugs and more run time and then see how it works.

Hooken

Thanks for the extra detail

Your problem may be double oil. These motors do not add extra oil by themselves, you have to do it manually for the break in period. I assume you are now refilling with raw fuel to start to clear out this extra oil?

Starting fine is <U>not</U> an indication of a sufficient battery. To properly test a battery you need to measure its cranking amps by loading it up. A volt meter after it has rested for 24 hours is another good indication. What test did you do?

Your o2 readings would be causing loss of RPM but at least it is due to rich running, not lean!

I don't think you have a plug problem. I'd run it for a few hours after break in without extra oil and see if it clears up.

I use two different battery testers one is a carbon pile load test and the other is an impedence test battery easly passes both tests. As far as the double oil your right I am now adding straight gas to it and will run it to see if it clears. New plugs are cheap so when I know its back to just gas then they will go in. I still want to know what the O2 numbers should be at idle. I think it is interesting that I have been told in automotive systems for almost thirty years now about the things that will kill an O2 sensor and Yamaha blows all kinds of junk at it and thinks it will live.

Pretty sure, once the engine is warm (o2 sensor is warm too) it should centre around 300mv at all speeds as long as the load is constant (it has been a long time since I checked and sold mine a year ago. Sounds like your battery is OK and you have the gear to test it properly.

I'd be intersted to see if it clears up without changing plugs, would you be prepared to hold off changing plugs just so you can let us know?

Yes I will let you know on Monday. Going to make a flat out run on Sunday 15 miles or so that should clear it out.

?

Runs great 74 mph gps. Still going to replace plugs and get that prop reworked. Then recheck