You can only adjust the idel circuit on this type of carb.
It could be a few things.
1. Fuel pump is not set correctly, the push rod height needs to be set to get the correct fuel delivery pressure to the carb, I can remember off the top of my head what it suposed to be, the measurment is with the pump off rod at max height and measure from the top of the plastic rod guide with gaskets to the top of the rod. If the rod is set too long it will pump excess fuel in to the carb and cause over spill and rich running.
2. The valve that closes the float bowl to the carb could be faulty ie not shutting the flow of fuel even when the floats fully up, again causing fuel over spill.
3. Is the choke set correctly ie is it opening fully when engine warmed up, if not it will cause ritch running
4. It could just be burn oil as the engine is new and the rings will be bedding in.
As for setting the idel mix, turn the fuel screw fully home not to tight just till it seats, then back out 2:5 to 2:75 turns (this is base setting for the fuel screw. Then adjust tickover using the bigger air screw to around 850 rpm +/- 50 rpm.
Next turn fuel screw in till you get the highest idel the back out a quarter turn, then reset rpm with air screw.
Also worth checking that the throttle position screw on the throttle are is set correctly, it sould be just off the choke cam when choke fully open, ie the distance of a cigaret paper.
