Changing the sprockets would be the cheapest and easiest mod. One tooth smaller up front or 3 larger in the rear. This will gear it down and help keep the rpm's up in the powerband. If you go with the larger rear, you'll have to extend your chain. A flywheel weight will smooth out the powerband hit giving you more tractable power in loose and wet soil. It will also help with the lugging ability at lower rpm's. I've done these two mods to a kx100 and really liked it. Then there are aftermarket pipes and silencers, reed valve spacers, low tension reeds, and pipe rings. I don't believe the cr85's have exhaust power valves and that's a real killer on low end. :( They are made to be screamers.