I have a friend who also has a Warrior but a 2003. His bike seems slow so he drilled his air box. It seems to be running lean. Any suggestion on jet size with stock pipe?

 

I wouldn't expect it to need to be rejetted at all just from drilling the airbox, but jetting is going to vary depending on altitude and temperature so it's hard to say. It's just going to have to be trial-and-error on this one.

 

Is it possible it was jetted on the lean side to start with? He race a 2003 Lakota Sport 300 and was dead even until he hit the top end and this concerns him. I am unable to compare it to mine because I bought mine not running and it already had an header and exhaust and was already rejetted accordingly.

 

You'll have to check the spark plug and make a judgement yourself. If the ceramic part on the tip of the plug is white then it's probably running lean. The target color is tan, and if the tip is black and sooty it's running on the rich side. It's possible that it could be lean due to your altitute or climate, but there's no secret formula to figure out what jet should be in it or anything like that..