I have a Karcher as well. I have also been having pressure problems.

My normal routine begins with running water through the section of
hose before connecting it to the Pressure washer, to clear any crud
and air. Remove all kinks and try to make the hose as straight as
possible. Similarly make sure the washer gun hose is also as straight
as possible. This normally resolves really bad pressure problems or
the switching on/off cycle. However mine has started leaking water out
of the plastic vents as well now. Anybody know what this is? I suspect
a gasket of some description needs replacing.