2009 KX540

[supertuner]

So I bought a 2009 KX250F in a box for cheap and put it together , was ok but unimpressive and just kinda uninteresting so I started looking at options for improving the performance and some how during the wee hours of the morning awhile back I found this site and was immediately drawn into the 500 2-stroke idea. So here I am weeks later still lurking around and trying to gather as much info as I can, then BAM. I just jumped in {probably head first} to a KX540 build. 250f motor listed on Ebay. So here it begins. Bear with me as I'm still figuring things out on this site. {like pictures} http://imgur.com/a/W65HS

[sandblaster]

Hey supertuner.
Welcome to the site.
I edited your post to show the picture.
Go to your first post and edit it.
Then look at the code for how I inserted your picture.
Keep the pics coming.

[supertuner]

After 120,000 posts read between this site, KXGURU, Thumpertalk, MacDizzys two stroke, supermoto ect. I'm currently re-building motor and getting a list going, may not be a 540 as I was told, crank appears stock with 88mm bore that is scored but ran with good compression. So first I will be replacing all lower end bearings, c-clips and using OE crank seals. Cases lapped, de-burred and cleaned but not sandblasted, new rod and piston will be a Wossner, very mild porting mostly just clean up intake and smoothing sharp edges entering transfer ports, {no raised ports} before re-plating at 88mm,kips bolt mod, Vforce-2 reeds with 10mm spacer,head de-comp,  and most likely a flywheel weight as most of my riding is woods/mx.
I will be using service Honda fmx gnarly pipe.

So, I have a some questions...
1. Was the ported piston actually found to be effective? {port size and position that is best?}
2. Are C2 or C3 bearings preferred? {keep in mind I live in Minnesota and have never been to the desert}
3. Recommendations for crank assembly and balance?
4. Fill decompression reliefs in transfer ports or leave them before cylinder is plated? Head will have de-comp valve and possibly re-chambered but must be able to use 91 octane fuel.

[supertuner]

Just a little update, new wossner rod installed and balanced with 88mm wossner piston, all new oem bearings and c-clips are here, cylinder off to get replated, new service honda pipe came in but still no silencer..

[reklessj]

Just a little update, new wossner rod installed and balanced with 88mm wossner piston, all new oem bearings and c-clips are here, cylinder off to get replated, new service honda pipe came in but still no silencer..

Awesome you should be up n runnin in no time

[umberto]

88 mm x 86 mm gets you a 525.  I went the same route, and love the 525 in my 03 KX250 conversion.  It sound counter intuitive, but everything I've read says you will need to run your carb leaner for the larger bore size.  I had to really go down in size on the needle (5x to 3x) and lean out my power jet in my Lectron to get it jetted correctly.  Now that it is lean enough, the bike is a blast to ride.

[sandblaster]

Bigger bore, leaner jets.
Your sucking a greater volume of air through the same size opening in your carb, what happens? Greater air velocity.
With greater air velocity you will suck more fuel out of the carb, more then you need for the larger bore, requiring smaller jets.

[sandblaster]

1. Was the ported piston actually found to be effective? {port size and position that is best?}
2. Are C2 or C3 bearings preferred? {keep in mind I live in Minnesota and have never been to the desert}
3. Recommendations for crank assembly and balance?
4. Fill decompression reliefs in transfer ports or leave them before cylinder is plated? Head will have de-comp valve and possibly re-chambered but must be able to use 91 octane fuel.

Missed this one.
1. The koolaid man says about 1 hp gain at mid to high rpm.
2. There has been some debate about this. We use OEM and hide our head in the sand.
3. Too late.
4. I wouldn't worry about it at this point, I'm sure your 88mm bore will be plenty.

On your VF2
If your running in the woods, use the low tension settings.
ALSO, REMOVE EVERY BOLT ONE AT A TIME AND LOCTITE THEM ALL.... Or bad things can happen.