Often when an engine is hunting, it's due to inconsistent fuel supply. Could be a blocked air vent in the fuel cap, restricted fuel supply from the tank to the carb, sticky or mis-adjusted float/float valve in the carb or dirty jets in the carb. First thing I'd do is check the fuel vent, follow the fuel to the carb to make sure it's flowing well. If all is well, there, check your float setting specifications. If all that is correct, it's time to pull the carb, completely disassemble it, including removal of the jets. Clean every component thoroughly, blow compressed air through all passages in the carb body, carefully re-assemble everything and make sure the float/float needle assembly is working right. While you're working with the float, get the specs for the float setting and ensure the float is set accordingly. It can make all the difference in the world if it's out of adjustment.