if you want to tune it correctly, start from step 1 and work methodically and for us to help you need to upload a video. Even though adjusting the wrong screw can improve it, it’s not correct. For example if you’re very rich on L and you compensate with lots of idle screw it may work, but it will affect the H fuel supply adversely because of it, you’ll have poor acceleration and lots of smoke.
Your issue could be too rich on H, to rich on L, or too low on the idle screw. However those carbs are often dependent too, they require the H screw to be adjusted first before the L screw.
Without knowing, start with the following.
Follow these steps if you have a tach
1). Obtain base setting for both mixture screws, and idle and WOT specifications from yourn service manual
2). Warm up the engine, and set the idle speed to spec. + 500 RPM
3). Tune the L mixture screw for the highest RPM obtainable (lean drop-off) while maintaining an actual idle speed at spec. + 500 RPM
4). Back out the L mixture screw to richen the mixture to bring the idle down to the specified idle RPM
5). Set the WOT RPM to the specification being careful to work from rich to lean while never holding the engine at WOT any longer than necessary to get a reading on the tachometer
6). Seat the limiter caps
Video here :
Or watch this video if you don’t have a tach:
