Taffy

the black knob is the choke.
the red knob is hot start.
the black one at the bottom right is the idle (tickover) screw
the one under the middle is the Pilot Screw. This photo is of an original brass screw that is barely visible.

I attach a second photo of an "extended pilot screw"

the correct name is pilot screw because you are adjusting the quantity of pre-mixed fuel air. you can't change the ratio - just the amount. as a general rule; when the screw is after the slide; it's a pilot screw.
if it is before the slide then it is either an air screw or a fuel screw. these aren't as good though as pilot screws.

if you have 3.5 turns of pilot screw you are running a very small PJ and a large PAJ. either way it is fecked.

Taffy

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gamer3210

In my case, there is this brass screw in the carburetor, and how well do I understand it should be set to 3.5 turns ??

gamer3210

Does the needle have a needle position adjustment, if so, what position should it be?

shrubitup

Depends on the needle. There are stock settings, yes. My manual says second clip from the top.

Taffy

Gamer!!!! the pilot screw should not be far from 1.5 turns out and if it were 3.5 there would be a problem with the jets in the carb.

you set the PS to what the engine wants not what someone here is telling you.

also, the needle; rich is better than lean (for no problem running) so you want to be in clip 6 of 7 from the top. this is a healthy start.

You need to tell us which carb that you have too.

Taffy

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gamer3210

this is 2 pictures you added keihin fcr 41 mx with acceleration pump

gamer3210

4122A serial number on the carburetor

gamer3210

update, the carburetor turned out to be worn out, the inability to set idle speed is the main symptom, the cost of regeneration in Pl is 75 eur