Raw Water System

[JVS]

Has anyone run across this problem?  I have bubbles in the clear hoses between the heat exchanger and exhaust riser.  When I raise the engine rpm I lose the raw water all together and the engine will over heat..  I have been through the raw water system from the intake up and can't seem to find anything wrong..   It's a d2-55 volvo.  I'm pretty frustrated !!!!