05 yz 450f will not stay running

You reported that most of the items I would've suggested, you have checked...
Good job.
A couple more things:

• Replace fuel filter, it's in the gas tank
• Check and clean the Spark Arrestor screen at muffler, when they plug up, it's a major restriction to exhaust gas flow
• And check and adjust High/Low screws at carburetor, video attached.
• And clean or install rebuild kit for carburetor

Good luck...

One more...

Wide open as in wide open throttle?? You mean the engine is racing? Something is wrong with the throttle controls, or the throttle valve in the carburetor may be sticking open. Look down the carb throat. At its base will be the throttle valves-"butterfly" valves just like the choke valve on top of carb. The throttle valve should be closed at rest, or at idle, or when gas pedal is not moved. Rotate the throttle lever on the carburetor by hand (when gas pedal is pressed down, the throttle is rotated). The throttle valve at the bottom of the carb should open and close with the throttle lever.
If the valve is sticking, spray some carburetor cleaner down it, and spray the outside clean, too. Work the throttle back and forth to make sure it is free to move.
For a high idle, have the carburetor adjusted. Timing should be checked, too-that can cause a high idle, but wouldn't cause it to go wide open.
Let us know what you find. Good luck.

Kescorpio56:
Check your throttle and choke settings. Something is causing the throttle plate in the carburetor to remain open or the governor is improperly set. I would reset the air/fuel mixture screws to one and a quarter turns out and back the idle screw all the way out. Make sure that the throttle cable operates the throttle properly and check the governor setting and reset the governor setting if needed. Start the engine and adjust from there. When the engine starts, adjust the idle screw until the engine idles. Adjust the fuel/air mixture screws for the best idle. Then run the RPM up and adjust the fuel/air mixture screws for the best run/idle combination. Don't forget to adjust the governor if the engine runs too fast or too slowly.

clean the carb

Sounds like your carbs are clogged, leaving choke wide open or staying on throttle to force running conditions merely tries to bypass the pilot jets but ultimately the carb needs to be thoroughly cleaned and if the gas is pretty bad you will need to flush your fuel tank out as well.

I would suggest a new plug and fresh gas and oil mix.push the primer bulb 8-10 times and turn choke to full.pull cord about 4 or 5 times until it starts.if it don,t stay running turn choke to half and pull cord until starts should stay running.let run for about 10 seconds then turn off choke.Almost forgot that during this whole process you hold throttle wide open.

sounds like you might have some trash in carb being a clogged pilot or main or needle seat in not letting in the proper amount of gas check all passages and use fresh gas if it has been sitting

SOUNDS LIKE THROTTLE NEEDLE STUCK OPEN CHECK THROTTLE LINKAGE STICKING OR RETURN SPRING

purchased new unit