OK , if the gas sat more than a month get rid of it , pour it in your lawn mower or car , it will run fine in them , you need FRESH Premium for these bikes to run ,period
When it runs does it pop thru the muffler at all when the gas is let off ??
If it does then i would bet the jets are clogged , if they are you need this
http://www.crfsonly.com/catalog/product ... ts_id/4294 , if you dont want to get the cleaner tool , then buy a new Pilot Jet , , also you need to make sure its jetted for your elevation , if you just bought it and it came from somewhere with a major elevation difference it will need to be re-jetted
$ Strokes have a Fuel Screw instead of a Air Screw like 2 strokes , in leans the mixture , out richens it , it is at the bottom front of the carb , you might have to tilt the carb to get to it , i would start at 1 1/2 turns and go from there , if you have to go in to less than 1 turn , its too rich on the pilot jet , if you have to go out more than 3 turns , its too lean on the pilot jet , its kind of hard to get at , so getting a Flex Jet makes life so much easier
http://www.crfsonly.com/catalog/product ... ts_id/2792 , it puts the screw on the side of the carb , by the idle screw so you can just reach down and adjust it without any tools
If your going to work on it yourself , you need to buy a Factory Service Manual , you can get them here or at your local dealer , dont get a Clymers , its not as good as the Honda Factory Manual
http://www.crfsonly.com/catalog/product ... ts_id/3226
After you get the manual , you need to check your valves also , just because it kicks hard does not mean the valves are not out of adjustment
For checking your valves you need this
http://www.crfsonly.com/catalog/product ... ts_id/5034 , its made to get into the tight space to check the valves , its too hard to get a regular automotive one in where you need it
Welcome to the world of 4 Strokes

, lol , once you get the hang of it , maintenance is a breeze