changing main jet is easy
1st thing is to unplug the fuel and hold it pointing up, so nothing is comming out of it. then to empty the bottom piece of the carb, by unscrewing the screw witch is at the carb under the gascable.
2nd thing is to turn the carburator upside down, and take off the bottom piece (witch is now the upper) by loosening 3 screws.
3rd: you should now see the main jet in the middle of the top piece of the carburator, and it can be unscrewed with a flat screwdriver. put in your new main jet, and assemble it again.
4th: pump the kickstarter and the el-starter untill it starts... if it doesent, or if it runs badly, try another size jet.
DO NOT UNSCREW THE WRONG JET, AS IT BROKE WHEN I FIRST MADE THAT MISTAKE.