Found the below on another forum....
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Author is "Yogibear": Have you noticed that the little 90cc atv's have very little suspension travel. My son's 2002 DS90 has 2 inches of travel upfront and 2 inches of travel in the rear. I was getting very disappointed watching him drive and bouncing all over the place. I looked for aftermarket rear mono shocks. Nothing, at least not at a reasonable price. I remembered visiting a local E-Ton dealer and noticed that the rear suspension had 4 -6 inches of good travel on their 90cc machines. I looked at the setup and low and behold it is identical to mine. I ordered the rear mono shock for $62.00 shipped and installed it on my little bomber in 10 minutes. Wow, it's like a new machine. Good, smooth, clean travel and no other modifications. How easy is that! I don't have the product number, but they ordered the 2004 rear mono shock off of their 90cc machine. The local E-Ton dealer was more than willing to offer me some help with this modification. My son is excited to go riding since he won't be bounced off of the trails anymore. Great little machine. Mounted a speedometer and light kit on it. This little baby will top out at 31 mph. Plenty fast for a little machine.
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If you are looking for better suspension in your DS-90, you may want to investigate his rear shock improvement. Might work for you too....
Hope this helps...