My 60 hp mariner starts, idles & runs excellent for about 30 minutes,then acts like it is running out of gas.It is on a Fisher pontoon & has a built in 30 gal.gas tank.It is not running hot.When it does this I tried squeezing primer bulb & didn't help.The primer bulb feels kind of spongy feeling & never gets full feeling.When it does this it will not stay running over 3000 rpm.Then I can let it set at dock for a few hours & it is fine for another 30 min. or so.This is my 1st outboard so any help will be appreciated.this engine has less than 100 hours.