no
it will be to easy to pedal
Yes
yes
"Needed" isn't a suitable word. Any tooth count will work, and only rider experience can say which will work best for him/her. 20T is fairly small, so I'd recommend a small freewheel too, to get any kind of speed out of the bike.
Yes, it will work. If it'll be the best for you or not is another question.
Any size will work. What'll work best depends on what you want it for. Higher top speed - go for a big sprocket. Quicker off the start - go for a smaller sprocket.
they don't make a 9 tooth freewheel they make a 9 tooth cassette and its better to get a 8 tooth as you can see heres a gear ratio for you to look atPopular Gear CombosSprocketF/W or Cassette2282382592810301133123613391441154416
You must have replaced a part. Either the Driver, Sprocket, or backrim. Your ratio isn't set right. with a 16 tooth driver you have to have a 32 tooth sprocket (i think. it might be 36) with a 9 tooth driver, you have to have a 25 tooth sprocket. i don't know how many spokes you need in your rim for either one though. go to a local bike shop and ask about it. sorry i couldn't help much. i havent messed with bikes in a while.
22 or 23 tooth sprocket will work. 23 will give you more top end speed for cranking at those huge gaps, while 22 will give you easier acceleration.
The 14 tooth crank gear mated to the gearbox 59 tooth gear gives a ratio of 4.21:1 which is found by 59/14. Front sprocket 11 & rear sprocket 47 gives a ratio of 4.27:1 ie 47/11. Overall ratio is found by multiplying the two ratios together 4.21*4.27=17.97:1 NOTE - The 14 & 59 tooth gears will be the primary gear reduction in a motorbike, this does not include the actual gearbox ratios which will need to be taken into account for the overall final ratio.
"would it go faster if i put a bigger cog on the back wheel" no, you need a smaller "cog" or sprocket on the back wheel to up the speed, but your still only looking at a 3% gain in top end speed. try a larger sprocket on the front eg. if you have a 15 tooth sprocket change it for a 16 or 17 tooth. this should give you up to about 10 to 15% gain at most. if you want a bit more then you'll need to look in to rejetting the carb, free flow airfilter, change the cdi for a race or unrestricted cdi, and a free flowing exhaust to help it all on it's way. but remember that even after all these mods your still only looking at a small top end gain, after all it's still a 125cc. if your looking to bring the speed up even more than you need to find a good big bore kit, but that's a lot of work and not one i'd recomened a novice to install.
some part wheel such as lever bar carb tires hubs sprocket's chains grips and top end will work but use a older one.
Nope, too much power, will blow the engine. the text above is retarded how can changing the engine blow the engine if a 70cc engine will fit it will work what he's saying is that the rear sprocket is to small. You would have to get a bigger sprocket so the engine won't run at high RPM's when you take off. With the bigger sprocket, the engine will have to work a little more to get the wheel to turn.