Surging can be cause by too lean a mixture. Since you getan improvement with the choke, that could be your problem. Did you try to enrich the mixture? Turn the power jet screw(the big screw over the fuel bowl)out an eigth of a turn at a time and see if that improves it.
You may have an air leak around the carb metering section that is the root cause of this problem. It can be at the carb throttle shaft, at the connect flange between the carb and the intake manifold or between the head and the intake manifold. It can aslo be caused by a cracked manifold. Take some starting fluid and with the engine running CAREFULLY spray around the throttle shaft, the conect flange and the manifold to head connections. If the engine speeds up when you spray in a particular area, you found the leak.
I would urge you to correct this problem ASAP as the exhaust valves can be burned from running too lean.