Re-valving is not really neccessary unless the suspension is really unworkable in stock form (not the case with an RMX). You will get much more for your money by simply installing the correct springs for your weight. The proper springs will hold the bike up in the stroke, keeping it from riding down in the stiffer portion of the travel and becoming harsh. Unless you weigh 150 lbs. or less, that RMX will benefit greatly from stiffer springs. You should have the suspension serviced regularly, of course, as a part of routine maintenance.
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1992 KDX 250-FMF porting,two-stage power reeds, Fatty pipe, Power Core silencer,titanium rod,Wiseco Ultra-lite, Pro-Action suspension...Oh my Gawd, they killed Kenny!