1.) SBP expansion chamber from Pirate cycles or of coarse Sick Bike Parts
2.) If your engine has the Aluminum intake get the Manic Mechanic Ported intake or the Stock steel intake for it and if you get the stock steel one get a dremel tool and grind all the rough spots out of it, that will help it flow better.
3.) replace the spark plug with an NGK B6HS
4.) get a high grade plug wire from Pirate or SBP
5.) Order new head gasket and then remove head and get a piece of plate glass at home depot or Lowes 8 1/2" X 11" in size or approx. then also get some 220grit & 400 wet dry sand paper and tape one sheet of the 220 paper on the glass with some duct tape nice and flat, then lay head on glass and then with very even lite to med. pressure move the head in a circular motion and remove 1/2 to 3/4 of the squish ring ( the raised surface sealing ring ) on the head and then finish it off with the 400 to give it a very smoothe sealing surface, also spray head gasket with copper coat gasket sealer for a good seal on the head gasket, doing all this will increase the compression a bit which will give the engine a bit more kick for helping to reach those higher speeds you're looking for.
4.) All of these things done will require that you retune the carb most likely so after you make any mods to exhaust or the intake you should run the engine a few blocks and then back, let it sit and cool for a few minutes and then remove and check the color of the spark plug to make sure it is a nice light to medium brown and not white which would mean the engine is too lean on fuel and too rich on air, clean the plug with wire brush and carb or brake cleaner between each test run after adjustments are made to clip on needle or jet resizing until you get it right, and you will pick up some speed by doing all or some of these mods. several MPH possibly and/or likely in my experience.
If nothing else do the Expansion chamber, plug and wire, this will help a bunch if you are still running all the stock stuff guaranteed..... this will give you more speed and more low end power as well, the stock mufflers are very restrictive on most of the kits and are huge power robbers on these little engines.
put a smaller sprocket on the rear whel like a 40T or 36T this will help if you do the expansion chamber and intake for sure, dont go with a 36T and not get away from the stock exhaust, the engine will likely not pull the 36T very well unless you free up the exhaust especially
Best wishes.....
Peace
