Could be some dirt still there. Be sure the choke passages and needle are all clean, replaced if worn, and installed correctly. Check the slide upper chamber seals are all correct. I've seen more and more incidents similar to mine, carbs pouring gas into the air box and cylinders. I reommend all O rings replaced at 5 years. My carb gas leak and flood to cylinders, was due to the float valve seat assembly O ring. Be sure to look passed your slides to the butterfly, and check for any gas pooling. Gas will leak passed the piston into the crank, contaminate your oil. Before I found my problem I changed the oil 5 times, and got good at yanking the gas lines off the pumps quickly. I'm pretty sure at idle, the butterfly's are fully closed, and gas/air is through the bypass. The point is if you have this flooding, gas will pool at the butterfly, you may get an idle, but when you tap the throttle you are dropping that gas into the cylinder, and will hesitate struggle.
If you may have had ethanol gas in the sled, it could have left algae everywhere. I found green residue everywhere. My problem over one summer, at the time the fuel stabil for ethanol was just coming out. The only way I could recover the carbs, was to servicte it, sonic cleaning, full tear down. I put startron stabilizer in everything that sits for more than a month, for insurance.
Good luck with the trouble shooting.