Help with overheating Volvo 260/290

[Hot Rubber]

RWC Volvo 260/290 runs at 215 degrees just running at fast idle.
This rig has new thru hull water pickup, new seawater pump impeller, new manifolds & risers, new volvo thermostat. I removed the water circulating pump and back plate to check for impeller debris, all clear.
I notice that the center passages on the intake manifold show blackening blistering of the paint. This carb has an electric choke so should the exhaust crossover passages be blocked?
I've changed to a mechanical temp gauge and get the same temp reading.
How can I find the cause of the overheating?

[1BIGJIM]

You said "new seawater pump impeller". Did you back flush the system to get all the old impeller vains? I know on Mercruiser they usually clog the oil cooler.

[Hot Rubber]

I removed all hoses, thermostat housing and circulator pump and backplate. only one small piece of impeller found in T/housing to circ pump hose. Impeller visable through hose nipples, looks fine.
BTW - the impeller and water pickup changeover were done by someone else. I did the manifold/riser replacements.

[Hot Rubber]

Also, when engine gets hot the hose from seawater pump to t'stat housing gets very hot.

[1BIGJIM]

Sounds like you might have something backwards?

[Hot Rubber]

If seawater hoses were reversed, no water would be fed to engine and it would not stabilize at 215 degrees. Looks like a simple, straightforward water flow system. Seacock to raw water pump to thermostat housing. The housing has permanently open passages allowing flow to the manifolds and flow to the circulating pump. Circulating pump pumps into engine block and water gets out of the block through the thermostat.
If the vanes of the circulating pump were sufficently erroded, could the seawater pump preasure be high enough at the thermostat outlet to prevent flow through the motor?