unit overheats above 2500rpm. Inspected manifold/riser (Osco). Found riser interior wall completely corroded out although water jacket still good. Good water flow at all other points in cooling system. 99.44% sure this is the problem (new riser on the way). This is an old riser that stands about 12" tall with a wall inside that separates the water inflow from exhaust gas coming in. Valves ok. suspect water backflow into exhaust manifold causing overheat. Anything else I should check?
