Unfortunately, whenever a carburetor is rebuilt, it still can be damaged or not cleaned thoroughly.
Before anything is ever done to a carburetor, one must see if the ethanol corroded any internal parts. if you take off the bowl and see a white corrosion on the metal parts, do not waste your time, just put a new carb on the unit. if it corroded the bowl, it corroded the internal parts as well.
To properly clean a carburetor, all of the passageways, jets and needles need to be cleaned out AND chased. i do not advocate using drill bits as this will remove metal and cause that particular circuit to be changed. I do not soak carburetors, i have felt it is a waste of time. what i do is remove all that i can then start spraying cleaner through the passageways. this way i know it is clean. if possible, i remove welch plugs as well. if a passage is dirty, use a piece of copper wire (a strand from a stranded wire) and push it through the circuits. do this also with the jets.
Unfortunately, doing all of the above still does not guarantee a working carb. the ethanol will eat the metal thus changing the metering of the fuel. this is when the surging happens. Honestly, it takes extremely very little etching in the carb to make it surge. most carbs have dropped in price and are simply not worth the time to try and fix. price it out and see if it is.
