Tom Langdon, of the Stovebolt Engine Company, has assured me that the hot water heat (about 195F) is adequate. The purpose of heating the floor of the manifold is to vaporize the liquid fuel droplets that would otherwise accumulate on the floor of the manifold, especially directly under the carburetor. Using engine coolant as the heat source should never cause the manifold to get too hot, which can be a problem with exhaust heat if the diverter valve gets stuck in the position.
