vacuum in Gas line 23 Scepter 1985, w 1997 225

[slantedeagle]

I recently purchased a 1985 Scpeter with a 225 Yamaha. It runs great but after 20 minutes a Vacuum is created the Ball in in the Gas line colapses and the engine starves from no gas flow. It's not the filter as I have repalced and the the problem persist and the Filter is always full of gas after it stalls out. Any thoughts on the Cause.