Hello, yes, carburetor o-rings are critical to be in a perfect shape and I'm pretty sure some fals air fets in the carb thru the o-ring which messes up the fuel-air ratio, making it imposible to work properly. Pit in a new O-ring and let us know the result

And for the choke please watch from minute 4:10. Choke cable works like this: when it's pulled, you restrict the flow of air in the carburettor. This helps enrich the fuel-air mixture, improving the ability to start the engine in low temperature conditions. And you pull/action it from your handle bar

@@thecurlyfixingguy7077 I know the principle, however, I wonder which part of the carburetor (likely the black plastic cylinder at 10:25 but how) is actuated by the choke cable?

Hello hello, I understand your question now. Answer is: the end of the cable that gets into the carburetor has a restrictive brass pin in the top which, when actionated, stops/closes an air channel thru the carb/ or opens an extra gasoline channel so you enrich the mix. It doesn't work with the black pipe, that is for vacuum creation for the main jet needle

​@@thecurlyfixingguy7077 Thank you! I ended up in a local bike shop as it turned out it is not a carburetor fault (probably something related to ignition coils. Once a bike is up and running I will learn it anyway.