The air-fuel ratio can be changed using the air-fuel screw; the main purpose of the screw is to change the ratio of the air-fuel mixture. The mixture can either be lean or rich, a lean mixture is one that has more of air than fuel and a rich mixture is one that has more of fuel than air to put in broadly. The other screw is the Idling screw which is used to set the idling rpm of the engine.
Now comes the tuning part, first the important thing you must understand is the direction of rotation of the screws. The air-fuel screw turned clockwise gives a lean mixture and when turned counter clockwise gives a rich mixture. The idling screw when turned in (clockwise) will give a rich mixture and when turned out will give a lean mixture. Before you start tuning you MUST make sure the engine is warmed up. Take a quick ride before you start tuning the carburettor which should sufficiently warm the engine. Turn the idle screw till the engine rpm reaches about 2.5k. Now our aim is to make the mixture as lean as possible at the same time not stall the engine. We do this by rotating the air-fuel screw clockwise to the point where engine receives its leanest mixture. The engine might stall during this process but do not mind, with practice you will get it ;). Now the mixture is set to the leanest condition possible which means the engine is receiving a mixture with more air and less fuel. Next step is to set the perfect air-fuel ratio, we do this by slowly I mean very slowly turning the air-fuel screw counter clockwise. The rpm should increase gradually and at a particular rpm, the rpm needle will show become constant. Now that’s the point where we have our perfect mixture. Now try to start the engine and try riding it, the throttle response should be a little crisper and accurate. The method is all about trial and error, with due time you will be able to get the right feel from riding and from the engine sound.
Hope this article helps and happy tuning:)
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