After rechecking my answers it is hard to get clearer than saying intake side versus mouth of the carburetor, but if you really want simple, watch the video, then you might understand. I did go back and highlighted the terms mouth and intake side and for what it is worth, the mouth is where air goes in, the intake side is the side where the intake port of the head is. I also highlighted the notation that it also relates to CV type carbs similar to the 34mm CVK stock carburetor.

Of course if you want to believe we're all lying to you that is your choice too. I'm just relating what I've learned since around 1972 to date. In that time I have NEVER seen the reverse situation with a fuel screw at the mouth or the air screw at the intake side. It really isn't nuclear physics or anything. They just don't put labels on them. Of course they do label kick starters and shift patterns on the cases... but makes me wonder if the person that needs those labels really should be riding since the shift patterns are now universal and even all on the left with new bikes. Always found that humorous.

 

OK, what does the OP have an 'air screw' or a 'fuel screw'.
Don't know that one do you!

 

It's not an air screw because it's controlling fuel flow through the pilot jet branch passageway.

Idle mix screw, OR fuel screw

 

On my carb it is a "fuel screw", so you know what manf & model the OP has?

Best to just call it a "mixture screw", then your always, 100% correct no matter what the situation.

But..... if your at the limit of the screw, you really need to know what it is.

 

He has a 2010 KLX250 so the carb's a Kehin CVK .

Why the riddles?

 

OP was the one confused. I was agreeing with him.

 

Yes, carb OEM 34mm CVK (mods, jetted per signature)

 

I don't really care, it isn't important to me.

He wants to know what the screw is. A few of us relayed our knowledge, you questioned it as if we were feeding him a line, so I gave the definitions per Mikuni (Kiehin are the same, as were the Amals, Bing, and IRZ that I worked with) so he can look for himself and figure it out.

Makes more sense, he's the one that needs to know. Now he knows if the screw is too far out or in what to do with the pilot jet regardless of what kind of carburetor he has on his bike in the future. He has gained some knowledge.

 

Actually Mikuni calls the actual parts either an air screw or a pilot screw and it does seem to depend on location and function as far as direction to turn for lean/rich mix.

The air screw is at the mouth, in front of the slide (based on direction of air flow for those who are picky about the terminology) controlling air jet flow, if Mikuni is being accurate in description by name.

The pilot is at the intake side behind the slide apparently controlling the pilot jet flow, again if Mikuni is being accurate in description by name.

Their terms, not mine. Doesn't really matter to me other than to know which direction goes leaner or richer so as to know if a pilot jet needs to go bigger or smaller. As you say, they control the idle fuel mix in the long run.