This is a Poppet Valve Replacement on a 2004 150hp OX66 EFI........
Replacing Parts: Spring, Valve and Gasket
Yamaha Part Numbers: 6G5-12416-00-00, 90501-16M11-00, 6G5-11382-A1-00
The location of the Poppet Valve is on the back of the engine, between the cylinder banks down on the bottom on the engine below the Wire Loom.
Parts you need to remove is the Wire Loom Cover (black cover on the back of the engine) Photo 1:
The 4 screws you will remove will be black like these:
Remove this cover:
Next remove the wire loom screws:
The 4 screws look like these:
Now slide the wire loom up (orange arrows show the direction, the green arrow points at the poppet valve location)
Here is the location of the poppet Valve Location right under the wire loom once you slide it up:
Remove the two screws and you will see the spring:
Remove the spring and OLD poppet valve: (here is a photo of the old poppet valve and spring setup)
Now replace with the NEW poppet valve and spring setup (the mushroom side goes IN towards the motor and the internal rubber grommet):
The eastiest way I found to do this by myself was to keep the wire loom raised at all times, put the new style mushroom head in towards the motor, put the gasket on the back piece and then put the back end of the spring in the cover and then by hand angle the spring into the back of the mushroom head in the motor and push forward a little, check to see the poppet valve and spring are all alined properly on each side.
Now once that is aligned and in, you need to slide both screws in on each side and make sure the gasket is lined up on the back cover and try to thread one of the screws in a quarter of the way and then the next. Once again make sure everything is aligned properly. Then tighten the screws halfway side to side and do not tighten one screw all the way and go to the other side, keeping the gasket aligned properly.
The end result is the motor pissing lazer beams: