I just picked up an 03 XR 100 for my wife that has a Big Gun slip on pipe. It was running just fine until my oldest son (15) decided to try and 'tune' it in and startred to messed with the air/fuel mixture screw on the carb. Now the bike will only start if you don't turn the throttle while kicking starting it and seems to be lacking power. The plug looks ok. I currently have the mixture screw turned 3 1/2 turns out. Is this where it should be set at?

Any help would be appreciated...

 

lol is that the only thing he messed with on the carb if so start the bike up and turn the screw until it seems to idle correctly and make sure the choke isn't on and the petcock is on also...let me know how you make out...also check the idle screw to make sure it is high enough

 

I think the general rule is to start 1 1/2 turns out and tune from there in 1/4 turn increments. I would make sure the idle adjustment is set low. If the slide is open too far and the mixture screw is way off, you will have a hell of a time trying to tune the thing. So to start, set the mixture screw 1 1/2 turns out, back the idle screw out, get it started and warmed up and set the idle, then adjust the mixture screw. Good luck!