I have 150 johnson and I have had the carburetors rebuilt, changed the plugs, fuel line, checked the filter on my gas line and have come to no answer.

What is going is the boats starts easy and idles fine. When throttle up it seems like it is running at half throttle even through  you have the throttle wide open. Then all of a sudden it opens up and runs like a champ. Occassionaly it might start to lose power and it like it is starving for fuel. I have checked everything but the fuel pump. Help me please.

is your vent open and clear on the fuel tank?

could it be flooding?

Did your boat shop set the timing by doing a "link and sync" after they rebuilt the carborators?  If the carbs open at different times and the timing is off it will run erraticly.