What is the Briggs model number of engine? How many aftermarket carburetors have you tried? When you say “none of the aftermarket carburetors have worked” , what exactly does that mean? Engine won’t start and run, starts and dies, hunting and surging?My Briggs needs the original Briggs with the primer hole in the right place for my Cub Cadet SC621. None of the aftermarket carbs I have tried will work. Since this carb is nla perhaps someone has a rebuilt or used one.

According that PN was superseded to 790120. Ignore the first two charactors as that is a left over when I was a Sunbelt Outdoors dealer.
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The problem is there two version on the net referencing the same PN.
Which version do you have? That would help narrow things down. And that way someone can contact Briggs as to which PN it should be.