I understood you.
You are talking for the screw that is located in the part where the throttle servo arm is attached.
For that I a made a hole on the side of the cowl, about 1 cm diameter. And right now the cowl is not installed before I resolve the issue of the engine.

I bought this engine from the internet, that is why I am "experimenting" with it.
And besided that I am working always with local experts, members of my club.

And regarding settings with the needles I wasted a hole summer with this engine, and there is nothing to do.
Even my club members told me that the engine is behaving in a strange manner.
The only thing that should be tried is to close that small hole. Bare in mind that there is another slot that lubricates that front bearing.

Thanks for the help my friend