'07 250 Roached cylinder. Go big bore or no?

[scallywag]

'07 KX 250.  I've popped my engine and it needs top and bottom.  The cylinder and head are not pretty.  I race intermediate XC, woods, desert, and would love to move the power to the bottom end a bit.  I've been thinking going big bore and having some porting done but in my endless searching I can't decide what to do or what will even work.  I need the cylinder fixed either way so going big bore isn't that much more $$.  Some guys say 300 kit, others say the ports are in a different configuration and it won't work.  265 is about as big as you can go?  Why do companies offer a 300 kit if it doesn't work?  I need to get this figured out so I can get out and ride!  What say ye?

[zz3gmc]

If you want to get some more bottom end get a 05 head or have yours machined and the squish reshaped to add compression. Kawasaki dropped the compression in 06 and it lost some bottom end. I have a 07 also and its weak off of the bottom. Im going to send the head out soon for a little tweeking.

[motoguy46]

Zz. Always respect your opinion. . But I would like to improve on your response. 05 and 06 take the 0034 head and 07 takes the 107 head and the 108 is optional

[motoguy46]

I have the 0034 and 0107 head, and they are subtly different. But IMho I would recommend getting which ever head you already own and have the  squish adjusted to your liking with respect to gas choice elevation etc..but the original poster is going to want/need to get head mods anyway to run a  bigbore

[motoguy46]

I think it the consensus that among most that 265 is the biggest you can safely go on 05 to 07..but there are at least 2 companies that advertise larger kits..and one company  I ..well no comment..i do like the idea of running a non custom  off the shelf wiseco 68.5 piston..I would like to get pinnonsaults  and others opinion on how large it can it go and why..but at this point .I wouldn't even consider it unless I had severe cylinder damage.

[KXDINO]

I been working on 06-08 250 lately this is what we been trying out on the engine ,these mods are for a wider and more powerful engine take 1.5mm spacer in the power valve governer and replace with 1mm spacer ,03 kx250 optional part ,team green porting specs plus porting on the inlet side ports for low down ,take 16 thou off bottom of cylinder ,take 4 thou off the head ,you should measure squish before and after machining, check for detonation if you have to take a bit more off the head ,one more thing match the cases to the cylinder ,these mods work ,jet to suit .We also run a full pc system .

[zz3gmc]

Didnt know it was only the 07. Should have bought an 06! Learn something new everyday!

[don46]

I tried the 301 big bore from Kustom Kraft, he said he had done lots of big bores on 250's but mine was the first on the new style cylinder. The first time it didn't make it out of the garage before it self destructed. the second time it ran until the first time the throttle was twisted, not more than 10 minutes,  there was no third time, it is in a box in the attic with the head. The ports get really close together and end up catching the ring and tearing them up. Maybe somebody has it figured out by now but its not for me, fortunately I found a cylinder on this site for reasonable, a guy had bought it for a 2002 thinking it would fit, when it didn't he sold it to me for what he paid.

So, if anybody wants to either try the big bore or sleeve the cylinder, I have the whole top end, including the head and power vavles (I think) that I would sell reasonably.

[scallywag]

Looks like I'll go after the smaller of the big bores.  Or maybe even just track down a stock bore cylinder and get some porting done.  If 300 generally equals problems, then I'm not going down that road.  Thanks guys.

[scallywag]

Sent it off to Pro Circuit so they can work their magic on it.  They convinced me (which wasn't hard) to stay stock bore but get porting and head work done.  I'll keep you all posted on the results. 

[Foxx4Beaver]

I use to have Pro-Circuit port/case match all my 250 motors through most of the 90's-early 2000's....man did they rip after they had their hands in there!...I never once had to think about going big bore on one.

[treedodgingfool]

After looking at an '05 cylinder we're rebuilding for someone that was sent & recieved back at the same time as my 300BB '04 cylinder (also own a stk '07), there isn't enough meat in that cylinder in my opinion to do a big-bore (pv & o-ring).  Also, IMO a 265BB would seem like a waste of money for the barely noticeable power improvement (300 is worth the bang for the buck).  Porting & head work would be all I would do with the newer "R" model powerplants.

[treedodgingfool]

I went BB on my '04 since the saddle time on my hubby's 500 (250SF/500 frankenbike) had me really chomping at the bit for the extra grunt, but since we haven't found a suitable donor 500 yet, we compromised on a BB.  For my application, it's the best of both worlds, granted it isn't a 500, but I can race it on pipe all day long in stick farms and if I want to be lazy and the let the bike do the work, I have the option.  The older "92-04" engines are a better platform for a BB, but I wouldn't waste my time with anything less then a 300.  I like the added traction when I want it and the extra helping of hit in the mid (allowed me to drop a tooth off the Rr Sprocket, 51 instead of 52).  Durabilty will be the question, though we're not competing much this year, I still have a few races I'm planning to attend.  I'll see how it plays out, but as of right now, best all-around bike I've ever ridden or built (spent a decade in the m/c industry, got to ride a lot of MX & Woods weapons, '04 KX chassis still my fav).  Sorry for hi-jacking the thread...   



...As for the '07, the best off-road pipe I've tested in the FMF Gnarly.  Definetly adds a extra helping of grunt to it.  Well worth the investment.  Add a few teeth to the rear sprocket (mines at 13/53) to get the power lower in the gears & more useable in the technical stuff.  Otherwise, porting &/or head work.

[scallywag]

To follow up on this.... Just about the time I got all my parts back from Pro Circuit (took longer than I expected), I destroyed my back and was not real quick about getting my scooter back together.  I'm on the mend and have been messing with my 250 lately, though.  It's not as dialed in as I'd like as far as jetting and such but WOW, what a difference.  Honestly I was hoping it would be more 300-like so I could chug around the woods but nope, it flat rips!  Not what I was hoping for but I'm not gonna lie, it is a hoot to ride. 

[Foxx4Beaver]

To follow up on this.... Just about the time I got all my parts back from Pro Circuit (took longer than I expected), I destroyed my back and was not real quick about getting my scooter back together.  I'm on the mend and have been messing with my 250 lately, though.  It's not as dialed in as I'd like as far as jetting and such but WOW, what a difference.  Honestly I was hoping it would be more 300-like so I could chug around the woods but nope, it flat rips!  Not what I was hoping for but I'm not gonna lie, it is a hoot to ride. 

good to hear!!...though I'm not surprised. I had six motors re-worked by them over the years I was racing, and was never disappointed in how they ran/performed afterwards. JoJo Keller would send my motors in along with his Honda motors, because he's good friends with Mitch Payton, and Mitch has always had nothing but good things to say about JoJo, and I was lucky to have grown up living 5mins away from him, and rode with him at times ...not sure if that really had anything to do with why they ran so strong, but anyone that threw a leg over one of my bikes couldn't believe how fast they were, and I was always more than happy.