on the pickup tube. They get pugged with varnish really easily. They don't look plugged when they're plugged either. Depends on how the pressure.washer is set up. Is the carburetor mounted to the fuel tank? If it is, remove the cap and look inside. If there is a plastic tube going from the carb to the bottom of the tank that has a flare at the bottom, that's where the screen is. Usually you can add some aggressive cleaner like BG, Motorvac, or Top Engine Cleaner to some new gas and let it sit for a few hours and it'll disolve the varnish. Then dump it out if you're smart and put in fresh gas.
If the carburetor is mounted separately and has a fuel line, the screen is usually in the tank where the hose attaches, or there is a separate fuel filter (again, a screen) in the line.
Failing that, yeah, plugged main jet.