how do u rejet an '07 yfz450? seems to back fire and just wanted to rejet it etc to see what that does. i have an open lid too and was told i should rejet for that also. thanx

 

Congrats on your new 07. I pick mine up in 2 days.
First, put your airbox lid BACK ON until you rejet or you could run so lean as to damage the engine.
Second, If its spitting/backfiring back through the carbs when you just start accelerating, you are lean on your idle/pilot circuit. You will know this if the popping gets better with the choke part way on. On your bike, turn the fuel screw out a little. With the lid on, carefully turn it in and COUNT THE TURNS. Then try turning it out to where it was plus 1/4-1/2 turn more at a time till you get smooth running off idle (when engine is warm).
To take the airbox lid off and/or add an exhaust, you MUST change jets in the carburator.

 

Ditto, what he said.

 

yep and I would check your airfilter to make sure it is clean contantly sinc having the lid off will allow more dirt in and I would recommend and exhaust and airfilter

 

thanx for all the help guys!! i'm just gonna put the lid back on and rejet so it will atleast idle right. i have one more question. is it normal for me to gun my throttle and low rpm's and have my quad sputter and then take off a second later, seems to hesitate and then take right off. thats with the lid on or off too.

 

If its happening with the lid on, it sounds lean on the pilot jet. Refer to my tip on adjusting your fuel screw above.

 

where is the fuel screw located?