Upgrades for the 2003 kx250 engine

[stevea100m]

So I have an extra 03 kx250 motor that I got off ebay a week ago for $260. I mainly got it to steal the electrics from as my stator on my AF died. This has got me thinking of building a motor to put back in my steel frame to play with. I am looking for any sugestions to make it better. I have read a few guys switching to the 04 cylinder or changing the spring for the powervalve to the 04 spring. Any other suggestions? Mind you this is gonna be used for off rad stuff like harescrambles and enduros but will see the moto track from time to time

[The Flyin Hawaiian]

I stuck a 04 head, powervalve spring and CDI on my wifes 03. Now it has some bottom end. A stock 03 is a little light in that dept.

[stevea100m]

I did notice that. I do have a platinum pipe on the AF and it seemed to help a ton. The other thing Ive noticed is that it doesnt have much top end speed like the gearing is super short. Think I had the ICO on it one time and it maxxed at like 57 and my bother 03 kx125 clocked at 64. I had to go to a 14 countershaft and 48 rear to get over 65 and here in michigan down some of these 2 tracks when ur makin up time speed is ur best friend

[The Flyin Hawaiian]

Im running 13/51 and have never hit over 69 on either the 03 or my 04. My wife managed to hit 71 on her 03 with the same gearing. All my other 250s from the past have hit the low 70's with the exception of my 97 WR250 Yamaha. I was making up time after a particularly nasty tight section at a enduro and hit a ICO indicated 83mph! She has a Gnarly and a V-Force on her 03. Tryed a Enduro Engineering pipe from a 04 on her 03, which realy woke it up but had some jetting issues so she put the Gnarly back on.

[stevea100m]

chances are I know they guy who welded that pipe as he was the one who welded my frame but anywho yea i am definitely consindering the vforce for obvious reasons just tryin to broaded this thing out a bit