well my new to me 2004 yz450 was ok from the get go just had a few issues that needed addressed. flame out to cure this i installed a +16oz flywheel along with 13-51 gearing. with this setup it is amazing total different bike is it a xr600 no it will not lug like a big thumper but it is 3 times better now. it really needs a 5th gear but i can live with that. it has plenty of speed in 1st for climbing and the power is very controllable didnt seem to hurt the rev of the bike at all. but i did install a jd jet kit also and it really helped the bike as well most of the poping on decel is gone but i have a leak between the header and mid pipe so it will be there till i find a clamp. i think the pump mod made the most differance of the jetting it revs way faster then it ever did even after the flywheel im a big guy and before it would not power wheelie in 3rd now just crank it and over the puddles you go. i have some more tinkering to do to the jetting it had a little studer while crusing at part throttle and it may be a fuz lean on top with the 170 seems to stop pulling befor i think it should with the hot cams in it. over all i am very happy with the bike now.