3 hp. yamaha 3mlhs 1994 starts but wont run

my 3 hp 1994 yamaha 3mlhs intermitantly starts but wont run for more then a few seconds. i am in truuble a lot.i have two 3hp motor with the same problem ihave taken carbs apart on both, float valve working good. i have an internal 5 gal. fuel tank and just cant believe this would cause the carb boul to to go dry. which i think is the problem. help???

[boats.net]

Probably need to rebuild carb, fuel pump is part of carb and diaphram may be bad, clean all jets and passages in carb. Check fuel is coming through fuel shut off valve.