Hi Wypipo
As it's a new bike then you could assume that all jets and orifices are clean, float height is good and float valve is sealing correctly, but there's no harm in checking to be sure.
I guess your bike is just jetted too rich, I've heard many people complain about the same with new bikes. I suppose the factory just send them out like that to be on the safe side.
As far as I know that's the easiest way to remove the carb, by loosening the rear sub frame. Of course, if you're only changing the needle, pilot jet or main jet then there's no need to remove the carb. The rubbers can be loosened, the top removed, then the carb rotated. At least that's what I can do on my old 2004 model!
To start with I would stick with the 170 main, maybe you could go leaner but for the moment try and get the pilot jet, needle and clip position sorted. As Jakobi said, try the NEDW needle with clip at mid position. Depending on how that goes you could try going leaner on the pilot jet, one step at a time, so from 42 to 40 to 38. After fitting a different pilot jet set the Air Screw to 1.25 turns out then adjust in/out to suit.
I found the MOST IMPORTANT thing was to only make ONE CHANGE AT A TIME, then get the engine up to temperature and test it. This ensures you know if you're moving in the right direction and also helps you understand which component effects which throttle position. I also kept notes on what I changed and how it felt, but that's just me!
Have you found the Jetting Database on this forum, it's interesting to see other people's setups...
http://www.gasgasrider.org/forum/showthread.php?t=2162
I found this chart helped me understand which components effect which throttle position...
calibration_chart.jpg
Are you using a good quality, full synthetic 2 stroke oil? I mix mine at 50:1 (200ml oil to 10 litres fuel) which seems to be the standard and I've never had any problems.
When I bought my bike it started fine and ran, but there was no power, it felt flat as a fart, in fact that's why the previous owner sold it. I thought there was something seriously wrong with the engine but I was pleasantly surprised when I discovered it was just jetting!
Before sorting the jetting it wouldn't lift the front wheel at all, now I have trouble keeping it down...honestly!
Be patient and stick with it, it's very rewarding and well worth the effort when you have it running correctly.
All the best, Dave.
