The insulator stops the transfer of external engine heat directly from the engine to the carburetor thus causing vapor lock. This is especially critical if the intake manifold is bolted to the exhaust manifold for the transfer of heat to the intake for proper operation by preheating the fuel prior to its entrance into the intake ports. If the exhaust manifold is not bolted to the intake manifold and heat is supplied to the intake for preheating through another source, such as water, the insulator is not as critical because there is not a direct link to the external engine heat.
Joe
