1988 200 v6 fuel supply problem

I have an 18 gallon tank mounted under mi windshield. I ran a 175 mariner with no problem for years. I hooked the yamha to it and it runs fine until I get down to a half a tank. Then when I hit 4000 rpm for about a minuted it starves and falls off. I rebuilt the fuel pumps, put a new filter in. replaced the line to the back of the boat wit 3/8 metal fuel line. I still have the problem. I ordered a new fuel line and primer bulb, I hope that works. Any other possible ideas? Some times when I go to make a run, I have to hit the choke to accelerate or it wants to drop off.

When the engine begins to starve what's status of primer bulb....full or collapsed? If collapsed then you've got a restriction aft of bulb. If full, when it begins to starve start squeezing the bulb. If motor responds then it's likely fuel pump issue.