No you have to preload the spring against the cam on the straight end. A service manual shows how it is positioned. You can use any service manual for almost any 2005-2009 KX250F and look at Chapter 5 page 16 and see the drawing. It shows the proper spring orientation.
Basics....With the arm pointed up you will have the straight part of the spring pointing to about 7 o,clock and loop part of the spring on the out side of the arm on the cam journal side. It will have tension on it, so you have to hold it there as you replace the bolt and shield that holds it in place.
Remember that the spring will not have tension on it when you put it on the arm and the straight part will be pointing to about 2 0'clock and you have to force it to the 7 o'clock position when you slip the arm in place. Be sure you turn the straight part of the spring CCW when doing this to get the preload.
You may be able to locate a PDF manual on line. Do a search.
If you want to, you can send me your e-mail address and I will try to send a copy of the drawing to you.
Paw Paw