Disclaimer: I got this off the Honda forum... but it worked
after some research I tried this, first totally clean your atv, remove all the dirt and oil, and wax, then gently sand out the deep scratches with ultra fine sandpaper followed by 0000 steel wool, once all the scratches are removed or diminished, don't panic your plastic will look pretty bad at this point, remove all the sanding dust and cleans and dry the plastic, now with a small clean wax applicator or small terry cloth towel swath start applying Holloway House Quick Shine( available at walmart) its an acrylic floor restorer that really sticks to the plastic and creates a tough shiny finish. plan on applying several coats, I put about 8 coats on mine, the product drys quick so by the time you get one coat one its time to apply another, you can use a heat gun to speed the process, after the 3rd or fourth coat you will be feeling better! and the plastic will begin to look new again, the more scratched up it is the more cats it takes. After you've reached the desired shine its time for the most important step, after the finish totally drys (20-30min)
wax the entire surface with a high qualitycar
wax(cleaner wax) this will cut down the surface like rubbing compound on clear-coat and make the finish shine like crazy and increase the color depth, really rub it well and you will be in awe of the results, you should now have plastic that looks better than new and has a tough finish( this stuff is made to walk on) here's a before pic and pic of mine after process, good luck..
P/S: this is not permanent but lasted about 8 months first time and the u just clean quad and re-apply floor stuff and wax. I only sanded and smoothed my old foreman the 1st time, and my dad now owns that quad and it still looks good. HOPE THIS HELPS