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This is a guide on tuning the VX16/18 Nitro engine, this engine comes with a 2 mixture & 1 Idle adjustment carby, here are the locations of these screw adjustors:

Low Speed Needle:



High Speed Needle:



Idle Adjustment:



The top one above the air filter is the high speed needle which controls the fuel mixture at high revs, the 2nd one is the small screw below the air filter which is the idle adjustment screw. The third one is on the accelerator's pivot point, this is the low speed needle which controls the fuel mixture at idle and on take off. To start with the top screw should be set to factory setting which is 3.5 turns out, 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.