When you installed the new kit did you make sure you got gaskets/diagphrams back on in the proper order. If you installed a new inlet needle you should adjust the metering lever to the proper height. A metering lever tool for the brand of carb you have is helpful. You can check www.zamacarb.com
for further info.
Depending on the age of the unit, it may be necessary to check for carbon buildup in the exhaust port--to check that it will be necessary to remove the muffler. A lot of the time, oily buildup around the muffler exit is a tell tale sign of a plugged antispark screen or partially blocked exhaust port.
If the carb is cleaned thorughly and if the gaskets/diagphrams are installed properly with no blockage of the exhaust port, I'd take a look at the metering lever height.