Sounds like an internal carb leak
So it seems that you're not sucking fuel. If you've checked your pulse line for cracks and have found none, then I'd say the problem lies in the carb itself. It sounds to me like either the needle is stuck in the seat, a very clogged internal filter, or the carb is internally leaking, and sucking air rather than fuel. The needle/seat (N/S) is easy to check. Once the carb is removed, take out the four phillips head screws that hold on the thin square piece of metal that looks like a cover (with a small hole in it). This will expose the diaphragm. Carefully pry it out and you'll see the N/S. If your needle is stuck in the seat, you won't be able to pump any gas into the carb. Using the correct pitch phillips head screw driver, remove the little screws that hold the lever arm and remove the needle. Inspect for wear along it's sides. Equally importantly, inspect the seat (the bronze barrel that the needle slides into). Check it for wear on the cylinder walls. If worn replace. If the diaphragm is hard and dried out, I'd buy a genuine Mikuni carb. rebuild kit (they're not very expensive), and carefully go through and replace all the old gasket components. I will clue you in to the fact that the N/S does NOT come with a carb rebuild kit. They can be attained for $20 at most places, like shopSBT.com. NOTE: do not use pliers to grab the N/S by the it's cylinder wall. This will damage the wall, and permanently ruin the N/S. I usually take the carb apart and apply compressed air to the back of the N/S, holding my hand to catch it as it shoots out
To check the internal filter, the other side of the carb must be removed. If you don't plan on replacing components, I'd be very careful to remove these as gently as possible. The filter is a small, plastic basket that sits in a hole on the main carb body, directly opposite of the N/S.
If I were you, I'd just get the new carb kit, and the N/S and just rebuild the carb, it's not hard. Just make sure it all goes back together the way it went apart. If you do decide to rebuild, reuse your old N/S spring so you would keep the same pop-off pressure.