Suzuki DF 140 falls on face when accelerating

[jgso]

I have a Suzuki DF 140 which sometimes falls on face when accelerating. I check the fuel bulb and it is slack. I pump it back up, motor runs fine until i TURN IT OFF AGAIN FOR ABOUT 20 MINUTES. Then bulb is slack again.

I have replaced the bulb and fuel lines from hull to engine twice, no improvement.

Ideas on what/where I am losing pressure?