250HP OX66 O2 Sensor and Timing

[Reel1Fishing]

Hello everyone, new to the forum. I usually post in another forum but figured I would also ask here since its geared towards Yamaha engines.

I currently have an 00 250HP OX66. Currently it has sort of a “lean sneeze” and surging around 2200-2500 RPM. Since everybody says to check the O2 sensor, that’s where I started. I did the idle/cover hole on intake test and recorded a little video. How fast are the numbers supposed to move within the range? Should I clean/replace sensor?

https://youtu.be/KZ-lGlqkDak

Second question is about timing. Don’t have a winky blinky so wanted to confirm if I had a bad sensor and timing was off. I know its supposed to be at 7*ATDC if its running correctly. There are two ranges on flywheel (negative and positive). Where exactly is 7*ATDC? My timing is currently at the orange line (750-800 RPM):

47EF9CD5-97D0-40AE-9BA1-9D03B28BF180.jpeg

Things I’ve done:

-Replaced VST filter
-Replaced LP fuel pumps
-New Spark Plugs
-Tested Coil Caps
-Cleaned Injectors
-Adjusted Oil link
-Decarb “Dunk” Method with seafoam
-Checked gas (no water/non-ethanol)
-Swapped Stator/Pulsor coil from spare engine
-VST has fuel pressure under load (35-36PSI)

Thanks for any help or info provided,

Jay

[Reel1Fishing]

Forgot to mention that the timing goes to the left of 1TDC and rpm increases to 1200 when I disconnect knock sensor. So I'm assuming my timing is correct (so to the right of 1TDC is ATDC and to the left BTDC).

[99yam40]

that sounds correct to me

[Reel1Fishing]

that sounds correct to me

Thank you for the reply. Any guesses on my O2 specs from video? I had read it was supposed to go down to .3 and up to .8 fairly fast when I would cover the intake hole.