its running weak mate these trekkers run weak from new and if you have made it a bit quicker its going to need more fuel.ok these have a gay gurtner carb on usually and there is no circlip on the slide needle,so you need to find the carb (just above the kickstart)take the air filer off and then you will see a cable going into the top of the carb (not an electrical cable) a wire one with black plastic coating it goes into a small plastic part undo that and then pull it out of the top of the carb.then slide the cable out of the slide by pushing it down into the slide and taking the nipple out of the slot then you will see a small white plastic locating plate inside the slide take that out and then take the needle out.ok now you need to find a very small washer to go over the needle but make sure it fits niceley in the bottom of the slide.the washer needs to be about .3 mm thick make sure the needle is slid though the washer and then refit the neelde and slide and cable ect... i bet its ok after doing that.
adam bike doctor, September 2010