Kx250 1999 engine performance upgrades

[swordcombat]

Just wondering what people advise on tuning my kx250 engine
As the cylinder needs a re sleeve anyway so was thinking big bore kit also i have a boyesen
Reed block , is there any ways to fine tune it like port the head ?
And tune the gears?

[Foxx4Beaver]

Just wondering what people advise on tuning my kx250 engine
As the cylinder needs a re sleeve anyway so was thinking big bore kit also i have a boyesen
Reed block , is there any ways to fine tune it like port the head ?
And tune the gears?

what type of riding are you planning on doing with it?...this can play a role to some point.

[swordcombat]

Well mainly just forest riding of sorts , im not a go fast as humanly possible person
Sort of enduro riding i guess

[Foxx4Beaver]

not that what I did to mine will work good for you, but...
all I did to mine was clean up the casting flaws, threw in a Wossner piston....and a complete pro circuit exhaust...and it absolutely rips.

*EDIT*
mine's a 2000, which is pretty much the same bike.

[swordcombat]

not that what I did to mine will work good for you, but...
all I did to mine was clean up the casting flaws, threw in a Wossner piston....and a complete pro circuit exhaust...and it absolutely rips.

*EDIT*
mine's a 2000, which is pretty much the same bike.

Casting flaws as in the cylinder head buddy , like were the reed block goes , also yeah mine has a pro circuit rear pipe and getting the same expansion chamber , also regarding piston im guessing mitaka is not a wise purchase?

[Foxx4Beaver]

Casting flaws as in the cylinder head buddy , like were the reed block goes ,
im guessing mitaka is not a wise purchase?

yes, where reed block goes and throughout all the transfers and ports.
I've never used Mitaka...but someone else on here might have some input about them.

[swordcombat]

Casting flaws as in the cylinder head buddy , like were the reed block goes ,
im guessing mitaka is not a wise purchase?

yes, where reed block goes and throughout all the transfers and ports.
I've never used Mitaka...but someone else on here might have some input about them.

I guess a dremel is my friend in this case 
Yeah heard bad things regarding miaka so i will go wossner i think , also crank needs
A rebuild but i may get a whole new wiseco or wossner crank as here in uk a full bottom end kit is £210 but to have mine rebuilt with a wossner or wiseco con rod is about £165.00 plus my crank has seen better days to be honest

[sandblaster]

Go Wossner on the rod and the piston.... You won't be sorry...

[swordcombat]

Go Wossner on the rod and the piston.... You won't be sorry...

What are the wossner full cranks like? Are they balanced properly

[sandblaster]

You buy a rod kit and have your crank rebuilt with it.
You can send your crank to a rebuilder and have it balanced.

[Friar-Tuck]

Hey SC,
  I just went through a 99 kx250 a few months ago for someone at work, once you get the piston /crank/bearings sorted, look for excessive play in the powervalve parts.
   The bike  had been rode hard and put away wet, (Heck it was 15yrs old!)  the clutch basket was pretty well notched and the fibers were burnt.
  I'm sure you will have a good look at all the internals, as we also had to replace third gear and several bearings and seals.
My buddy had ordered a bunch of parts before I had gotten the engine torn down and ended up in a budget pinch. 
   The forks needed seals and bushings, the swingarm and suspension bearings and seals were toast and the throttle was falling apart along with the cable.  Brakes and rotors oy-va... I guess what I'm saying is make sure you have a good final parts list before getting the "Goodies."
      All I did to the engine was cleanup the casting flaws,roughed up the intake and matched the ports.
    (The sizing of the ports were a few mm's off and it wasn't done on purpose) .   
    There was probably 3mm or so of play in the main valve and the exhaust barrels would not line up correctly no matter how I tried to time them.
We had to replace all the powervalve parts,  My buddy couldn't understand how only a few MM's could make such a big difference, until he rode the bike with everything working...   
He had a steahly flywheel weight, Boyesen superstock reeds, aftermarket air filter and an fmf pipe and silencer.       
   He did say he was gonna change the gearing as the stock set-up was just a little to fast in the woods we have around here.
Sorry to prattle on...
 Blaster & Foxx have a lot of experience and both stand up guys, their word is good as Gold.
   Tuck\o/

[swordcombat]

You buy a rod kit and have your crank rebuilt with it.
You can send your crank to a rebuilder and have it balanced.

Sorry i meant wiseco cranks as wossner dont make them , but reading up i hear bad things about wiseco cranks and some good things about hot rods , but may just get mine rebuilt , thanks for the advice buddy

[swordcombat]

Hey SC,
  I just went through a 99 kx250 a few months ago for someone at work, once you get the piston /crank/bearings sorted, look for excessive play in the powervalve parts.
   The bike  had been rode hard and put away wet, (Heck it was 15yrs old!)  the clutch basket was pretty well notched and the fibers were burnt.
  I'm sure you will have a good look at all the internals, as we also had to replace third gear and several bearings and seals.
My buddy had ordered a bunch of parts before I had gotten the engine torn down and ended up in a budget pinch. 
   The forks needed seals and bushings, the swingarm and suspension bearings and seals were toast and the throttle was falling apart along with the cable.  Brakes and rotors oy-va... I guess what I'm saying is make sure you have a good final parts list before getting the "Goodies."
      All I did to the engine was cleanup the casting flaws,roughed up the intake and matched the ports.
    (The sizing of the ports were a few mm's off and it wasn't done on purpose) .   
    There was probably 3mm or so of play in the main valve and the exhaust barrels would not line up correctly no matter how I tried to time them.
We had to replace all the powervalve parts,  My buddy couldn't understand how only a few MM's could make such a big difference, until he rode the bike with everything working...   
He had a steahly flywheel weight, Boyesen superstock reeds, aftermarket air filter and an fmf pipe and silencer.       
   He did say he was gonna change the gearing as the stock set-up was just a little to fast in the woods we have around here.
Sorry to prattle on...
 Blaster & Foxx have a lot of experience and both stand up guys, their word is good as Gold.
   Tuck\o/

Oh yeah dont worry buddy , this is a slow full rebuild and the parts in total come to about £1500.00 GBP , but i, doing it by spending £200 per month.
Well the forks i have completley rebuild with seals and bushings with fresh oil , every bearing will be replaced to.
The barrel needs a re sleeve and the con rod has no up and down play but
Lots of side to side play to the extent were the conrod has wear marks on from the sides of the crank.
Also power valve play? In that do you mean just loose in the port?
I was actually thinking of putting a 2002 barrel on my engine and buying the matching valves.

[sandblaster]

Wossner does not make a complete crankshaft but the picture I posted is a 99 KX250 Wossner connecting rod kit.
You can see our build here:
http://www.kxriders.com/forums/index.php/topic,15682.0.html
Rebuild your OEM crank and have it rebuilt with the rod kit.
It is as good if not better then the stock kit.
In my opinion you will end up with a superior crank then either a Wiseco or Hot Rods crank.

[Foxx4Beaver]

     Blaster & Foxx have a lot of experience and both stand up guys, their word is good as Gold.
   Tuck\o/

thanks for the kind words Tuck!....I've always had a lot of respect for your answers and input as well.