Yesterday, I worked on the exhaust manifold and would like to know how the heat riser tube installs. The photos attached are of the top and bottom of the manifold showing the holes the heat tube fits in. The heat riser tube would fit in the top hole and then connect to the automatic choke on the carb, the engine exhaust then heats up and this heat rises through the tube to the choke and the choke begins to open. But, how is the bottom hole sealed? Thanks for the replies....Jeff