I'm not familiar with your bike..
A choke is some sort of metal flap that prevents air from getting into the carb, and could be seen inside the throat of the carb.
When starting a cold engine, applying the choke makes the air:fuel mixture very rich and the engine is easier to start.
Once the engine warms up the choke is released. It is usually controlled by a manual lever or by a cable. If it's cable operated it's cable might be joined with the throttle cable or it may have a separate control lever..
If the choke is always closed, very little air can get in even though you turn the throttle.. the result is a rich mix and the rough running symptoms you have.. and top speed could be low like under 10mph.
A choke normally functions when either wide open or completely closed. (part way open might be good for really cold starts on cold days.. at least till the engine warms up.) It's cable and/or lever would be adjusted to get the full range.. It must be wide open for normal running... a partially closed choke upsets fuel mixture.
I asked if you filled the fuel tank before this started because i was thinking the fuel could have been very old or polluted or that you made a mistake when adding oil.. like adding way too much.
_but i emtied the bowl and then tried it and still felt flooded_
not sure what you're saying but if you emptied the bowl and got the same symptoms, maybe the symptoms are from a lack of fuel.
Unless you can think of something you did right before the problem happened, like change a fuel filter or switched mufflers or installed a new spark plug or something else that could have accidentally messed things up, dirt in the carb is most likely.
The only advice i'd have at this point is to do what you're planning on doing.. Check out the plug and maybe carefully clean that carb .. tighten bolts and nuts, check cable adjustments and stuff..