After landing hard off a jump my YZ 250f isnt running right, like its not getting enough gas

SOURCE: how much oil for 2003 yz 250f fork seals

3 Pints is average but you can adjust it to your riding style and weight. Stock oil height is around 130mm from top but you could set it around the 110 to 100 range for increased bottoming if you do a lot of big jumps ect.. 5w oil is the usual weight but fork oil goes up to 20w.
-John

SOURCE: How to tune a 2005 yz 250f?

ok buddy on the carb will be 2 screws turn the idle one out to lowen idle and screw the mixture one in 1/4 of turns until it stop backfiring and thats it buddy 

SOURCE: looking to change the spark plug on a yz 250f, how

Sure??. You should have a long spark plug spanner in your tool kit.Remove the plug cap in the middle of the valve/rocker cover.Blow down hole with compressed air.Insert the large end of spark plug spanner down hole and turn until it engages around hex . Use the spanner from your tool kit,turn anti-clockwise untill loose then use your fingers to turn the tool and WWWWWWHHHHAAAALLLLAAAA. 1 removed spark plug...Most important to blow and foreign material outta da hole as we don't want any nasties falling into our nice new engine . glad to help.please leave feedback.

SOURCE: My 05 yz 250f clutch wont engage..

is this while its runnig or not, sometimes the cluctch wont engage while the bike is not runnig, but will engage when running. its common. if not they may just be stuck. did you drain the oil and have the plates exsposed to elements while the engine was out of the frame. open the clutch plate cover, check that they look fine. other than that if the clutch is hydrolic check for air in the system. and also the fluid level. good look.

SOURCE: 2005 Yamaha YZ 250f. suggestions on type of motor oil.

What did Yamaha tell you? I think 10 is too light. Call your Yamaha shop for the proper recommendation.