After riding the box-stock KX500AF for just a lap, I wrote up a list of a dozen changes that I thought it needed. And I knew just the man to help sort out my issues — Richard Wilk of MX1 Suspension in Roseville, California. Richard had helped me with both my Hondas and KTM's over the last few years, so I handed him my list and we set about ironing out the trouble areas.

Forks: A lot of the KX500AF frame’s cornering issues were caused by insufficient low-speed damping (insufficient for a 500cc engine, but not for a much mellower 250 four-stroke). MX1 increased initial low·speed compression damping to achieve a higher ride height, which allowed me to turn under diesels at will. MX1's fork revalve eliminated the midstroke spike, but could handle bottoming resistance with ease while still using the standard fork springs. Increased rebound settled down a busy front-end without packing on downhills. The MX1 fork revalve cost a modest $195.

Shock: The MXA test riders had installed a stiffer shock spring already, so Richard Wilk increased the rebound damping to match the new spring rate.

The million dollar question: Can I go as fast on the Service Kawasaki KX500AF as I can on a modern 450 four-stroke? Yes—at least for a few laps. Could l win on one? I did win my class at the amateur portion of the Glen Helen National and made the top five in the younger age groups. And if you put a 21-year-old Chuck Sun on the KX500AF (which is how old I was when I won the 1980 AMA 500 National Championship), I think I could have won the 2009 Glen Helen National—and I'm not talking about the Two-Stroke Challenge.

For more information, go to www.chucksun.com or www.mx1suspension.com.

Motocross Action, September 2009 pages 130-131