Check your engine RPM's, don't over run your engine it will ruin it. Check the right RPM on the pump. Don't use the pump at a higher rate than it is designed for, it will get ruined. Set your unloader (there are instructions here for that) then check a nozzle chart for your rated pump then buy the nozzles needed for the pressure you want. Change the pressure by the nozzles, not the unloader, you can ruin the unloader by adjusting it. You may not hit right on the money for pressure, but there isn't much difference in cleaning ability by 200 psi on either side of your target. If in doubt go lower. Keep in mind, more pressure, less flow.