90 hp Merc 2-stroke fuel pump delivering no gas to carbs but plenty to pulse hose fitting. Why?

-The fuel pump is rebuilt ( to specs, used mercury manual) and fuel flows through the pump but does not make it up into the first carburetor. Instead the fuel flows through the pulse hose into the powerhead fitting and down and out the third (bottom) carburetor. This is a serious flow of fuel which impedes the flow of ANY fuel to the carb linkage. If i block the pulse hose fuel makes it to the first carb. Is there a check valve or something connected with the pulse hose that could have blown out allowing large amounts of fuel to flow in to the powerhead fitting? It just seems as if something is missing since you can pump the ball as many times as you want and fuel just pumps through the powerhead into the 3 carb. Thanks For Your Help.