If you partially close the choke will motor run better - even if just for a few seconds? If so your problem is restricted fuel flow. To remedy proceed as follows:
1 - Remove the fuel line at the carburetor, then open the shutoff at the sediment bowl. You should get a solid stream flowing out the end of the line - not just dripping gas. If you don't, clean the sediment bowl screen and check for an obstruction in the shutoff valve. Also check for junk in the opering where the sediment bowl screws into the tank.
2 - If you see good fuel flow, the problem's an obstruction inside the carburetor - most likely something plugging either the float valve or the high speed metering jet. Disassemble the carburetor again and throroughly clean everything inside. Check and clean the screen (if there is one) behind the fuel inlet nut. Blow out all internal passages with compressed air before reassembly. Check for proper float level and make sure the float is not binding before installing the float bowl.