Fuel Problem

Hey guys, I am having a fuel problem on a 2000 Merc 350. Starting a couple weeks ago, my boat was hard to start when hot. If I took off the fuel/water seperator canister, it would not be all the way full. I'd fill it up, and the boat would start right up. It would run a little rough, but then it would smooth out. Then, yesterday, I went to start the boat, and it wouldn't go at all. This was the first time I tried to start it cold and was unable to do so. Anyone have any ideas? I'm thinking fuel pump or fuel pressure regulator. Would a faulty fuel pressure regulator prevent the boat from starting? or, is that more likely to be a pump issue? thanks in advance

My guess would be a weak fuel pump.

I had the same problem with my 02 Tige. Look for another fuel filter between the fuel tank and the filter you changed out. Changed it out and all was great.