What about a warped tank causing a leak?

Did you put in the screw under the throttle valve?
Also if the gas tank is warped you can sometimes use two gaskets.

I did put the screw in under the throttle valve, but the warped tank suggestion is interesting.... I'll throw another gasket on and see what happens. Thanks for the suggestion!

On those type of carburtors, you must have the air filter bolt in place or the engine will suck fuel thru that opening and flood the engine.

with the tank separated from the carburetor, check the mating surfaces for warpage. A precision steel ruler works well. A warped carburetor can be corrected by removing the two tubes and working against 400 grit on a flat surface. Must be careful.

If choke operation is marginal, consider using a repair kit 391413. Comments from other posters are all valid