": : : (this is on the carb.) OK, on most 2 cycle engines i have seen, there are 2 to 3 different adjustment screws. 2 for the mixute of gas to oil, and one for the idle. is this the same for a moped? and where is the idle screw on a 1980 motobecane?<p>If there is a screw with a spring, near the base of the carb, then this is the idle speed screw. It is tapered on the end. As you screw it inwards, the taper pushes on a block, a ""metering block"" I believe. Anyway, when you screw it in, the block slides upwards, allowing more air in, and hence more fuel. When you screw it out, the block is allowed to go down farther, and you will get a slower idle. These are probably the most simple carburetors you will ever see, and as far as I know, there are no other adjustments. Just keep them clean, make sure the jet is in good shape, and turn the screw for an appropriate idle speed.<p><p>"