I am fairly sure that the spring rates on the XR600 are lighter than the XR650L. I used to own a XR650L, I think that the spring rate in the front is fine. The rear was too stiff, it was sprung for carrying a passenger. The front end would dive, but it was partially caused by the rear end "standing up too much" because the rear was too stiff.
If I were you, I would do the following :
- Change the fork oil and set the oil level at the middle of the range specified in the owners or service manual. I prefer mine set at the lowest level, but you can make it stiffer in the last four-five inches of the stroke by raising the oil level (just like the progressive spring without having to spend the money on one).
- The XR650L fork has adjustable compression, with, I think, 12 clicks of adjustment. I would start at 8 clicks out. That is turn the compression adjuster clockwise until it bottoms softly (don't force it) and then turn it counterclockwise to the 8th click. The compression adjuster effects mainly the low speed compression (diving, etc.) Turn the adjuster clockwise if the front forks dive too much in the corners.
- Install a "lowering link" or go with a XR600 spring. I have heard of people doing both. I would go with the lowering link myself...
The "lowering link" was originally made by Bob Strode and copied by everyone else on the planet. You can get the suspension link through Bob Strode R & D in Woodenville, Washington, U.S.A at (503) 885-1108.
They are also available through White Brothers. I am sure that White Brothers would have an Eibach spring for the front forks as well.
For the terrain here, I prefer a straight rate spring. There are alot of roots and rocks here and the straight rate spring will soak up your
average 6 inch root with more compliance when the fork is halfway through the stroke. A good example of this scenario is when you are braking hard into a corner and hit a series of roots with a few 6-8 inch diameter rocks thrown in for good measure...
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