Carburetor adjust screws???

[robace78]

Ok so I have been fouling spark plugs and have come to find out it is because I need to adjust the jetting on my yamaha yz 125. So I think i found (2) different screws to turn. (1) I believe is the idol screw. When i turn this my bike actually idols now without stalling. The second screw is kind of hidden in a crack like where the air rushes in from the air filter. So basically where the air filter attaches to the carburetor area... what does this screw do??? I'm sorry for sounding so ignorant about this but i am a newbie... I ordered a service manual so i can figure things out. I am to believe that there may also be a third screw used for adjusting the carburetor. Am i right?? How should do i know what screw to turn and how much to turn it??? Any help would be greatly appreciated. Thanks for your time!!!

 

[Badgadjit1]

not sure about an 04 but my 99' has the air screw as a little flat head screw on the side and my idle screw is actually my choke ( instead of pulling the choke you twist it for my idle)

this may help also, read both, pretty important stuff for 2 strokers....
http://www.all-offroad.com/DirtBikes/Beginners/BGNov98.html

Scroll down there is a nice carb section you should read also
http://www.dirtrider.net/forums3/showthread.php?t=133452&highlight=Spanky's+jetting+guide

 

[robace78]

thanks dude!!! I actually think i'm starting to understand what's going on now. I can't wait for my book to come. I'm sure then i will fully understand what the hell jetting really is. Thanks for all your help!!!

 

[Badgadjit1]

ya i feel the same..heh...i have a race comming up this weekend and my carb is outta wack heh...i read those last night...

 

[NacNac250F]

All the little screw at the back of yur carb is is your air screw. It meters the amount of air that goes to your pilot jet. If you have to have it more than two turns out from seated then you need a smaller pilot jet; if you have to have it is less than one turn out from seated then you need a bigger pilot jet.

If you just started riding and your bike is completely stock, you are probably putting around and that is why your bike is fouling and not a jetting issue. But if you have an aftermarket pipe or porting then its a different story.

 

[robace78]

I do put around when i'm in the woods because i don't want to get killed but i also go all out in the open field.... i bought the bike used... it's a 2004 ... do you think i may need to change the pilot jet?? i have been reading up on the carb and is that a piece i need to buy to put in the carb or just by getting to the pilot jet i can adjust it by turing it??? sorry if i sound ignorant but i really am and i'm trying to learn here!!! Thanks for all the help!!!

 

[junkjeeps]

Pilot and main jets are rated by numbers. You would need to open the carb and see what size(number) jets you have. Then you can buy other size jets either higher or lower numbers according to what you need and change them.