I've been given an Excell vertical shaft 6HP (2 gpm 2100psi) pressure
washer.

http://www.ppe-pressure-washer-parts...xwgv2121-parts

It doesn't look like it's had much use and no obvious abuse. It has an
unknown history.

Runs fine but dies 10 seconds after running washer, not much spray
pressure.

I know nothing about pressure washers. Oil in engine is fresh, have
not yet looked in pump.

How should I proceed? I have mechanical aptitude and am fearless but
don't want to get caught in a death spiral. What should I be looking at?
When do I shoot it?

Jeff