I have a nearly new gas pressure washer with a pull rope that is impossible to pull unless the wand trigger handle is pulled. In other words without water flowing out of the wand the engine will NOT pull. If I clamp the trigger open and then pull the rope it starts and runs fine.

What can be causing this?

 

Common problem, often it's the unloaded valve.
What happens once you get it running and you let go of the handle?

 

Typical problem. Have you cleaned or cleared the nozzle filter?
I have Sears unit that it happens about once every season.