The carb top "seal" is, simply, a round, flat rubber gasket, nothing more, nothing less. Same is used on both the single cable, and earlier H1 tops. The earlier top was two piece, with register tab that fit into the recess. Remember, the early caps had both the cable and its adjuster, AND, the idle speed setting rod in them. On both types, there are "air leaks, both through the cable adjuster, and the cable end access hole in the bottom of the slide. The gasket clearly only serves to hold the cap in place on the single cable type, and helps hold the cable.idle rod plate on the early carbs.
All H1 carbs have the stop groove, as shown. The early two piece tops use that groove to locate a tab, to hold the top insert from turning on the carb, so the cable, and idle rod do not get mis aligned, which would angle the idle rod, causing slide to "stick" in its bore,
NOTE: The "gasket" is just that, flat rubber, NOT an "O Ring". Without the gasket, the tops, both styles, can loosed, and unscrew from the carb bodies,
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