It could be so many things
Does your linkage bind?
Heat Shield?
Return springs on the shaft and each carb? You should have both. I make and sell a return spring. https://www.m2racing.com/shop/p/lounge-tunic-/-cream-4l2xd
Does it only do it when hot?
One way to find out which carb it is. Take the dog bones off, blip each, see which one stays higher idle