I noticed a 200... actually 168.9 CC for sale through a scooter dealer on web. It has more power than a 150 but 19 more CC is not much more. So maybe if a stocked 150 does around 50 MPH, well the 200 would hit 55. I read up on this 200 CC scooter and the 150. The Chinese are copying what other motorcycle manufacturers do. Kymco has a 200 scooter listed 163 CC. I guess anything bigger than 150 is now a 200.
Well the scooter I like, still has hardly any body. Looks more like a motorcycle verses scooter. Has that same engine as the 150 but the engine has been bored out to be 19 CC bigger by the manufacturer. I looked up the manufacturer and looked at 150 to the 200 speed. A 150 done to the manufacturer a Max speed of 80 kmh. The 200 scooter done kmh. So about 9 MPH fast than a 150. It had a 13 inch tire back wheel. The manufacturers name was Dong Fang DF Moto.
Read where the only way to get more power, was to get more CC. That rejeting carb is only to make run cooler. That can put heavier roller weight in but that only gives one better take off performance. That can change the belt to a Gates belt but it will only last longer than a Chinese cheapy. But generally a 150 CC scooter will do 50 MPH on the flat. Now some scooters like the Zuma 50 with a two stroke engine can hit 40 MPH. Bigger tires have something to do with it and gearing. Something to do with weight, like if I weighed 300 lbs and raced a person that weighed 125 lbs, on the exact same model of scooter, well the smaller person would have an advantage on take off, be able to get to Max speed faster, be more wind resistant. Now people do bore out engines themselves. That is changing the CC that had origanally. They do this to create a faster scooters.
There are a few things you can do to a 150cc to get more speed/power.
I think usually the first thing to do is to get it to breath better. First by a performance exhaust and then larger carburetor and intake and of course a performance air cleaner. Get that engine breathing better. More air flow more fuel=more power.
Next would be ignition. Performance CDI, good spark plug, performance coil. Better spark curve and good spark=more power.
Now that you got more power how do we get more speed?
A performance variator of course. A performance variator is 115mm in diameter. This allows the belt to ride up a bit higher which gives you a little bit more final drive ratio.
Installing a taller rear tire, if possible, will give you a higher final gear ratio.
And you can of course install new rear gears.
There are some simple suggestions for more power/speed without cracking open the engine.