Well, firstly the idle set screw adjusts only the idle, it does this by limiting how far down the slide can go, thereby allowing more or less fuel to the engine - but only at idle. So while you do need set this (engine off, screw it in all the way gently & by hand - then back it out 3 & 1/2 turns for approx idle speed, then fine tune w/engine running) it wont do anything for a fuel/air adjustment. That is the small C-clip on the needle inside the carb - usually the second slot down is the average setting - but every motor is a little different, always check plug coloration when messing about with your fuel/air ratio.
Just wanted to mention that these china 2 strokes are renowned for running like crap until broken in. Mine was 4stroking (misfiring every other stroke) so bad for the first hundred miles or so despite all attempts at adjusting fuel/air that I considered junking the dang thing.
Now that I've got about three hundred miles on it - it's a night and day difference. I'm not suggesting that you shouldn't attempt to tune it in, I just wanted to reassure you that it isn't just a matter of mix - ya gotta ride the thing till ya bleed!
Spookytooth, Bikeberry, Sick Bike - most of this forum's sponsors are quite good if yer lookin for upgrades btw, and the performance subforum here is ossum
I would actually suggest replacing the carb with the following as the 66ers carbs are garbage;
CNS Aftermarket Carburetor for Motorized Bicycles w/ Adjustable Air-Fuel Screw
(air filter, cables, grip & kill inc) Price: $50.00
Spooky Tooth Cycles - Motorized Bicycles: Gas Powered and Electric Bikes - CNS Carburetor for Motorized Bicycles
Cheap muffler? I suppose you want an inexpensive tuned pipe... Though I don't much like the Machiavellian method or the various plumbing fixtures, this setup is one of the least expensive (also available in chrome);
Black Expansion Chamber Exhaust Pipe
[SBP-ES002] $64.95 Sick Bike Parts
however - for the money, this 'un is soooo sexy;
New SCSW Tuned Pipes for sale!
$120 Pipelyne Manufacturing. (408) 279-2307 http://motorbicycling.com/f23/new-sc...-sale-189.html
Hope this was some help - just remember to get some miles on yer bike, not that it's much of a chore heh