18 ft. lbs.
Use a Champion RJ19LM set to a 0.030" gap.
HM80 stands for horizontal medium-frame 8 HP and HMSK80 stands for horizontal medium-frame Snow King(in other word a snowthrower engine) generally equipped with a looped starter grip for mittened hands, intake system that resists icing and possibly an electric starter that uses household current.
Actually, there are a few different possibilities depending on the exact model of your Tecumseh. Here are the most common models that were equipped with 8.0 HP engines, and the corresponding correct spark plug (note, part #s are for NGK brand plugs. If you go to an auto parts store or power equipment supplier, they will most likely be able to interchange the part # if they don't carry NGK). H80, HM80: BR4LM HH80, HMSK80, TVM195, TVXL195, VH80: BR6S Snow King 4-Stroke engines HMSK80: BR2LM