1999 F15 Carb problem

My 15hp four stoke cranks and idles great, but will take the gas when you try and increase throttle. It is also leaking gas from around the diaphram on the bottom of the Carb. Could the problem of it not taking the gas be a bad diaphram or do I need to rebuild the whole Carb? I honestly don"t know what the diaphram does. Thanks

[boats.net]

That is the accelerator pump. You would need to clean carb when remove it and replace diaphram.