Backfire through the carb can be caused by an exhaust valve too loose and not opening. Do you have stock valve train with pedestals or have the heads been modified for adjustable rocker arms?
Forest
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.