Its not the manifold. its either carb/fuel system, ignition or cam/valvetrain.
hard to troubleshoot a vehicle via e-mail. The previous posts have offered good advice. What do you mean the carb "SEEMS" to open all the way. Have you visually verified this? Are your exhausts very "sooty", indicating an excessively rich mixture?
George
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.