primer buld problem

[Big_Squeeze]

I have been out in my boat twice so far this month and have had this problem each time. I have an 88hp Johnson 1989 model and am running a portable tank. Last year when I bought this tank I ran ok with no problems. This time when I run WOT for 5 to 10 mins. my primer bulb stinks closed from the vacume. I thought I was pulling too much fuel but my carb jets are preset and can't be adjusted. I have to D/C my fuel line and vent then reprime. I have checked my fuel lines and tank vent all seam fine. What could be going on. My main tank has a nonrepairable hole and had to be removed. Thats the reason for the portable.