Was the outside temp somewhat cold? W/this intake there is no heat under/through the manifold. So the intake may get colder before it warms up. This will cause the fuel to puddle in the lower portion of the intake. Causing a lean condition especially under "light" throttle. The main metering system with 72 jets is right for warm weather but too lean for cold weather. Now you may have a blown power valve which leads to rich mixtures and real noticable at idle. But this will help "some" in cold weather. Long story short, replace the PV and jet up. That is if you are going to drive the car in cold weather. Questions? Is there a thermostat in the cooling system? Do you have a direct fresh air system hooked to the hood?
Definately fuel related...issues here!