Sounds to me like a blockage in the high speed needle or the spray bar. Flush fuel backwards through the needle valve, and pull out the carb barrel and the fuel nipple. Clear out all the fuel pathways. I've seen this behavior on my TT Pro 46, and when I cleared things out, I found a very small piece of plastic that had come from the fuel tank. Once it was cleaned out, the engine returned to its normal reliable self.

Brad