Is there any website where I could learn more about the relation between the jets, the needle (and its position), the airbox, the exhaust, etc... I would like to know more about how those things work together. Unless there is a brave one who would like to explain it to me...

 

here this should help...

 

Sorry for the small graphic but I couldn't find the larger one. It doesn't deal with exhaust but it shows what part of the carb comes into play at what throttle setting.

As far as the exhaust goes, if you go with any aftermarket pipe, or the stock KLX300 pipe you are letting the exhaust escape more freely, and in turn should open the airbox by getting the KDX200 snorkel, or removing the snorkel all together. Now that you have more air, to keep the mixture correct, you need a larger main jet to get more fuel into the system....

Figures Eric would beat me to the pic while I was searching for it.....

 

OK, why change the air/fuel screw if we control the air and fuel with exhaust, airflow and jets?

 

Cuz exhaust, intake, and jets are constants .... that can be changed but still constants, a/f screw is for tweeking and elevation changes.

 

and weather changes for that day.

 

I like this thread. I'm pretty baffled by all the talk of jetting around here, but I hope to get a handle on it someday. I can turn a wrench just fine, and understand the mechanical side of things pretty well. But jetting seems to be one of those things you can't simply figure out from just looking at it.

So, what is the straight diameter?

 

guess that I am lost as well. What is "the straight diameter"?

 

Well pilot jet isnt on that graph, so i think straight dia maybe the pilot jet....

 

But is'nt the slow jet (shown with the air screw) the pilot?