the stock carbs on these are designed to work with hella restricted air filter tract, then on the later models some of them have various emissions type bullshit that makes it even worse. they were lean out of the gate and the emulsion tubes have super small holes that corrode up over time.
the china clone carbs are just more robust, the chinese people making these things uber cheap know how to modify them so they are very robust, they kinda just 'always work'. probably don't run as well at all throttle positions or get as good of gas mileage, but they just seem to be healthier.
I installed one that was take-off from a xr70 clone kiddy dirtbike that had been upgraded and it ran great right out of the box. I feel like you have better chances with one that was originally sold attached to a bike because the manufacturer had a vested interest in making the thing run so they could sell it