Just so we are using the right terms, a 2 stroke engine doesn't have a cam. I think you are referring to the crankshaft which turns brown in any engine ran with some natural castor.

So back to the troubleshooting, you know you aren't running rich since the glow driver doesn't affect the idle RPM, so it's possible you are running lean. But if I understand you correctly, you have tried tweaking the low speed needle and didn't get it any better? If that's the case, I suspect a blockage. The fuel passage in the carb is small, so it doesn't take much to restrict the fuel flow. Occasionally there is something in the new tank that can get in there, or if you laid the fuel lines down on your workbench a piece of dust can get in them and make its way to the spraybar. A quick and dirty method to clean in out is to run the engine up to full throttle and seal your finger over the carb barrel. That sucks a lot of fuel through the spraybar which can dislodge the offending particle. Just be really careful of your fingers when you do it. If that doesn't work, check all of the bolts to be sure they are tight on the engine (they can work loose during the initial thermal cycling on a new one) and then re-plumb the tank in case there is an air leak in the lines.