Simple little upgrade on your Suzuki DR650 or DR-Z400, replace your lower chain roller with a  sealed ball bearing chain roller. This roller can also fit a number of other machines; check the size against yours.
 
The stock chain roller has no bearings and is just friction-riding on the bolt.
Reduce the friction dragging down your drivetrain
High-quality seals keep water and dirt away from bearings
Precision contact-sealed bearings
Polyurethane roller with 98A durometer hardness for long life
 
Replacing it with a roller on bearings makes for a smoother and quieter transmission while the roller itself last longer.
 
The roller is 34mm in diameter, 24mm wide, and fits on 8mm bolt diameter.