Basic MTB suspension adjustment
The 4300 came with a very basic suspension. As such it has very basic adjustments. The preload adjustment makes the spring feel stiffer by slowing the initial compression of the fork. There is no dampening or rebound adjustment which would control the speed at which the fork extends after it compresses. What you may be experiencing is the lack of rebound control. The preload is at its' max with the knob screwed in or turned counterclockwise until it stops. It is possible that either the knobs are broken or the fork has worn out if you see no difference with different settings. Unfortunately there are no parts available for these. Your bike has a 1 1/8&quot; straight steerer tube which is no longer used on higher quality forks. So your options are limited to looking for a older used fork or replacement with a size adjusted rigid fork.