The job of the carburettor is to provide the engine with the right amount of gas, in the correct mixture of air and petrol, at all times.
Many years of development have gone into perfecting the carburettor’s function.
The present section provides illustrations of older types of carburettors as well as illustrations showing how the carburettor works.
Idling screw almost all the way in, throttle needle in the 2nd notch from the needle’s point, main jet screwed all the way in, and loosened 1 full rotation.
Start the engine.
If it four strokes, screw the main jet in a little until the engine only four strokes slightly.
Then adjust the idling screw so that the idling speed is fairly high.
Now run the engine warm. While running along a straight and even road with no wind against you, adjust the main jet to the exact point where the engine stops four stroking.
Finally, adjust the idling speed so that the engine doesn’t stall when you shift into gear (though keeping the clutch in).
The throttle needle makes sure the engine gets the right air/petrol mixture at half throttle also.
So: Ride the moped at half throttle. Check whether the engine four strokes or seems like it’s dying.
After moving the throttle needle, the main jet and idling speed will need readjusting.