Looks to me like there is moisture in the fuel tank? Look to see if there is a drain plug for the fuel tank at the bottom. If so and if you can remove the plug without doing any damage I would drain the tank to see if rust and other stuff is in your fuel.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.