People keep doing a repeated search for, “four turns out from the seating of fuel screw of keihin 4 stroke carburetor do get more mileage in motorbikes.” The answer to this is no. The mixture screw should be correctly called the idle mixture screw, as it only controls the air/fuel ratio at idle. This screw should only be adjusted as needed to correct the idling of your engine & the very beginning of the transition off of the idle stop. And even then all other factors affecting your engine, such as spark & air should be checked & corrected first. Normally the only reason you would turn the mixture screw out that far, would be on a high performance engine that has been re-jetted for maximum power. Of course an engine like that gets the minimum fuel mileage.
On a stock engine if you turn the mixture screws out 4 turns you will develop drivability problems, and there will be an increased risk of engine failure due to overheating caused by an excessively lean mixture at idle. The other problem is that with the screws that loose is that you run the risk of them vibrating out and leaving you stranded. Plus your gas mileage will probably go down due to the way you have to twist the throttle to compensate for the drivability problems.
Since this is a popular topic amongst those who commute by motorcycle, sometime soon I will do a post on how to maximize fuel economy. Except for basic maintenance none of it will involve any work on the carburetor.

Peace Y’all