That sounds like every service call I've ever run. "It was working great before it quit".
Something that was working happily with no popping, misfires, stumbles, cutting out, or pushing of the car is no longer working as happily-- so what used to be is not as important as what presently is. As we are all trying to help without the benefit of seeing or listening to the car, moving in the direction of general weakness seems prudent... and Kadrons are notably weak in the needle and seat. His needle valve being fine last fall doesn't mean it is fine now.
It's either spark, fuel, or something mechanical-- it's a rule. My money is always on spark. But on the off chance it isn't, I'd move from there to the known weaknesses of the fuel setup
... or not. Your mileage may vary. I'm no good at this game, so I'm tapping out.