Call me old school but, I own a 1974 shovel with a ss super-e carb. I recently tore the entire bike down to have it painted and to fix all of my (or most of) oil leaks. Since i have put it all back together my tanks are vapor locking. I have to stop and blow into the breather side of my fat bobs to get it flowing again.
Now here is what i have tried: all new lines and filter, new gas cap with breather, and checked all the holes out of the tank including the presure line across the top between the tanks. Im at a lose for words or ware to go from here. If any one can help it would b great.

Never had this problem till i took it apart for paint.

 

So, you have pulled fuel line off the carb and turned the gas on and let the fuel drain into a suitable container and it still stops flowing? If yes then the problem is still in the tank/cap/vent area, if no and the fuel still continues to flow after a long time then the problem is in the carb. Best I can do from here.