You need heat in the manifold to help vaporize the gas until the motor warms up. There's a number of ways to do that, but the basic idea is to get heat to the intake manifold as soon as possible. Some manifolds have water jackets to take care of that, and often the plumbing rusts and people put plugs in the holes, not knowing what their function is.

Sometimes a "heat box" is built around the intake, using metal to form a box around the base of the intake and then feeding exhaust manifold heat into the box using either convection or a tube.

Paul Schmehl CI 6
geek@stovebolt.com
Stovebolt Staff: Geek