All engines regardless of the manufacturer suffer from a certain amount of tolerance stack up. This can result in very different settings on identical motors that is why some are telling you the factory settings are just a very general guideline.
When you start to turn the idle screw and the high speed screw it’s easy to get them out of sync and even if they almost appear to be set fine tuning can be allusive.
This method seems to work well for all non air-bleed carbs. These are the ones with the idle adjustment on the side of the carb usually in line with the high speed needle.
Turn the low speed out until it stops or almost comes out. At this point you do not want it to have any influence on the next adjustment. Turn the high speed in until it bottoms out but gently do not force you do not want to damage the needle or seat.
Now turn the high speed out the recommended turns in the manual. Usually somewhere around 2 to 2 1/2 turns.
Use a short length of fuel tubing and place it over the fuel nipple on the carb. With the carb open if you blow through it you should feel/hear air passing in the carb.
Using a 1/16 drill bit or piece of wire close the carb until the barrel just holds the wire/drill in place. Do not force or you will damage the aluminium barrel or throat of the carb.
While blowing through the fuel tubing slowly turn the low speed adjustment in. When the passing air stops back the low speed adjustment out until you can just detect air passing into the carb. You may not hear it but you will feel it with your mouth.
This is about your best primary setting to start your fine tuning from.
Start your engine and slowly advance the throttle to full. If the engine begins to falter clip the glo driver on. If it now will go to full throttle the high speed is to rich, if it quits with the glo driver attached its to lean. Adjust the high speed no more than a quarter turn at a time until the engine runs at full throttle. Richen it up slightly until a slight drop in peak rpm is detected.
To set the low speed reduce the throttle and bring it to its lowest reliable idle. Once it settles advance the throttle smoothly and observe how the engine reacts. Suddenly quits the low speed is probably lean back it out a quarter turn. If it loads up, smokes and struggles to get to full throttle rich so turn the low speed in a quarter turn.
Depending on the carb you may have to reset your high speed after adjusting your low speed. Checking it every so often while fine tuning is a good idea.
When you get to the final tweaking adjustments no greater than the width of the screwdriver blade may be enough to effect a change. Go slow and take your time.
When properly adjusted the engine should idle for long periods of time and advance smoothly to full throttle after and extended period of idle. Short periods of idle the engine should respond instantly to full throttle with a rapid throttle advance. The longer the idle the cooler the engine will be so go easier when you advance the throttle after longer periods of idle.
This works for me.
Dennis