looking at this, more than half of us backyard racers can't afford carbon fiber, magnesium components and the like. best bet is a set of scales, a stop watch and lots of practice time. momentum tracks, paperclip tracks, hard/medium/soft tracks, black clay/sand/peanut oil tracks....and the list goes on....none of it matters if you can't get a setup under you no matter what you weigh or how much you try to take off.....
first....get on the scales and get the numbers right for the class that your running and for what you feel comfortable with. even if it's 25 pounds heavier than what your shooting for. as long as your percentages and weight placement is right, then the extra weigh MAY be beneficial. get on the clock and see where your at....record lap times and all the other data that you need for setup....get back on the scales and check it again...adjust (adding or taking away and getting back to the right percentages)....and hit the track again....do this a time or five and you may hit on the best possible combination....whether it takes you to the front or drops you to the rear, only your driving style and others in the race will determine your finish.
but you can't just start cutting or replacing things without knowing positively where your at and the direction that your headed. if you can't get your kart to handle with all the things on it now, what makes you think cutting a bunch of stuff or replacing it with carbon fiber is going to make you faster? a lot on here has been said about removing weight and being faster...all of it good, not taking anything away from the other posters, but before looking at removing weight in an attempt to get faster, work with what you have and adjust your setup....then if all else fails to get you right, then start removing things or spending the money for the exotic stuff....
TIRES + MOTOR + SETUP = WINS AND PODIUM FINSIHES....you can't leave even one part of the equation out or your nothing but a back marker......