High, Low Needles and Idle Adjustment

Looking at the top of the carby, two screws will be visible. The high speed needle controls the fuel mixture at high revs and is inline with the air filter. The next screw is a smaller screw below the air filter which is the idle adjustment screw. Finally the third screw which is not as easily visible (low speed needle) is on the accelerator's pivot point, and controls the fuel mixture at idle and on take off.

To start with the top screw should be set to factory setting which is 3 to 3.5 turns out for the HSP cars, this is a rich setting but is good to start with. Then start the car, it may need some revs to keep it running but for now just take note at how it idles and if there is any fuel coming out of the exhaust. If there is alot and the car is struggling to run then turn the low speed needle clockwise 1/4 turn at a time until it runs a bit better. Then sit the car at a standstill and all of sudden give it full throttle, if it takes off well and there is some smoke then the low speed needle is set where it should be, if it stalls it is too lean and needs to be turned anti-clockwise. If it stutters and alot of smoke comes out the exhaust then it is too rich at the low speed needle. Once you get its low speed about right then give the car some revs, if it accelerates but then stalls it is too lean, if it is slowly accelerating and won't go into high revs then its too rich. Once you have the mixtures about right then you can set the idle stop screw, make sure you do this last because the idle will change each time you adjust the mixture so your just wasting time playing with it until the mixtures are right. You will know when it is right because it will hit very high revs and the power will be good throughout the whole rev range.