Motorized Bicycle Throttle Problem?

Wholesale Xiaomi Scooter from https://bitly.com/3pOuG8A

When youy open the throttle is there ANY response? (Change in engine noise etc). If not I'd suspect the throttle cable is not doing its job either because it is broken, not connected one end or the twist grip has failed. Go take a look at it  we cant

Starts perfectly but wont rev sounds like problem with throttle cable. A bad carb would make for hard starting.

Just Guesswork, you realize,  as we cant SEE it.

 I would go first with Anon's  suggestion,. remove air cleaner, force slide or butterfly up, see if  that fixes it. If so, cable off the throttle.. There is a hole  and slots to get in and guide cable, perhaps it;s jumped or broken off cable end or the plastic guide broken.

If no, turn off  fuel, remove fuel line from carb, with bottle underneath, turn on  fuel, Should be a Stream, not a dribble,. If restricted,  try taking fuel cap off.. Fixed? Check vent in cap. If not, drain tank, clean tap and inlet screen. May be rust in tank, so in that case, remove inlet screen, put in an inline filter.

Operate the throttle at the carb end with a pair of pliers, if that does help then your throttle assembly is not operating correctly, but they are a fairly simple mechanism you should be able to rebuild it.

exoplanet gave you the best answer

Could be poor ignition advance or the carb needs to be cleaned / rebuilt. Looking at it ain't good enough. I would state the age / mileage of the engine, check the advance, get a carb manual, rebuild the carb and add an aftermarket fuel filter. Also, you don't say if the bike's been sitting for a long time, whether the gas tank is rusted, etc. Hard to troubleshoot stuff without having all of the info, dude.

Turn the choke off. Put in a fresh spark plug.