Habbi wrote:
Can the output pressure of the small 4-6 hp gas pressure washers be
turned down? For example could a 4hp 2000psi/2.0gpm karcher be turned
down to ~1300psi? If not could the intake source be restricted to
slow the flow? I have a small electric 1300psi unit which is ideal
for my application but the gas one are not available in this size.

The bigger ( 11 to 16 HP) pressure washers have a dial to turn down the
pressure. Not sure about the 4 to 6 Hp, you might check them at Home Depot.