This is a easy one.
Trace the hose from the washer tank to the nozzles and find where it is kinked.
This is not the issue, one of the first things I did was check the hose. I was hoping that you were going to tell me that there is a filter on the line or a way to check if it was plugged.
Are there any coarse filters on any of the connections?
Rob, You stated the washer line was "partly blocked", that led me to advise you to check for restrictions in the supply line which I have found kinked in the past giving the same symptom as you describe.
I fully agree with Don, if the tank filter screen is not blocked and you are sure the line is open by all means check the nozzles.
Keep me posted.
I am traveling for work so it will have to wait until this weekend. I am going to try what you said.