Good points fellas. Correlation does not necessarily equal causation...
My neighbor is an old geek engineer like myself who is handy. I think in my case it was a stuck valve that I verified when I removed the bowl. The dark mixture was probably residue just sitting at the bottom of bowl.
Yeah you do need to be careful lending equipment to those who don't RTFM, especially pressure washers and letting the pump spin too long without moving water.
The stuck valve forced me to pull out my Honda GCV190, which was sitting in shed for 6 years. I burned out the pump cuz I left the engine running too long without moving water. Replaced the pump, but bought the Subaru and have been using that.
On the Honda I did a quick smoke test (checked it had spark) used a primer bulb gizmo ( made this and use all the time) to squirt some good gas into cylinder and see it would fire. It did, so then I drained gas tank/carb (fuel was bad) added fresh fuel, primed cylinder again and gave another smoke test. Took 4 pulls and it fired right up!!! This time I was lucky. Used for about 20 minutes then shut off and changed the oil.
Used again to finish up what I needed to get done. Now I have 2 pressure washers working again and would gladly let next door neighbor use cuz he knows what he's doin and he got me to move on the unit sitting in shed for 6 years. It was on the list, but was always pushed down on the list for 6 years.
I'd be careful lending pressure washers to those not handy, burning out the pump is pretty easy. Lesson I learned the hard way.