My 85' Evinrude 70hp won't stay running. I prime the ball and choke it, it runs until that little bit of gas is gone than dies. Basically it revs up and right back down to nothing, almost like it runs only when its choked. While pumping the ball and watching the fuel filter, I can see gas barely leaking to the carburetor, and the fuel filter is never full. I was thinking that the filter was pluged, but I took it off the line, gave the ball a squezze and gas came out freely on the exit side. The ball doesn't get completely hard either, just half way, and its not until half way and hard will the gas move in the fuel filter at all, and than like I said earlier, just leaks to the carb. Any thoughts?