big bore kit for a 2002 kx-125

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Dec 22, 2002
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#1
ok i sent my top end to eric for the 144cc big bore kit. i've searched the forums and read about the different stories that some of the previous big bore kits had to say,but my question is has anyone put the big bore kit really to the test on the track? i'm a 125 "b" rider and am looking for some help from this kit to help with the starts. this year with the motor stock and 12/51 gearing the yamaha 125's and 250 f's where killing me. so most of my races i had to work through the pack to get a middle of the pack or better placing. yes i know i'm crying and yes i do love to challenge myself by pushing harder, but i would like to take home just one trophy for all the preperation and hard work and don't forget money that goes into this love affair of man and machine. believe me i spent two weeks going back and forth on what to do, port job or big bore. so now here i am with the questions. if anyone has run your big bore on the track against some of the bikes mentioned and you where getting beat before what about now? another question how finicky are the big bores in realation to jetting? example temp change, fuel type,type of track{sandy,hard pack}and also what bolt on items you've added along with the big bore kit and how they affected the outcome. another question how far did you have to change the jetting{main,clip,pilot and air/fuel mixture screw} also where did you see the most gains from {top,middle or low end} thanks for any help that you can provide i'm a nervous nelly right now not knowing if this was a wise decision or a can of worms by going with the big bore. once again thanks. here's a list of my bike : 2002 kx 125 v-force reeds,main 340,pilot 40,clip 3rd pos.,ult. 2 fuel, pro circuit pipe and 304 silencer, 12/51 gearing and timing advanced.also i asked eric for te mo-better porting.
 

bclapham

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#2
Originally posted by angus
2002 kx 125 v-force reeds,main 340,pilot 40,clip 3rd pos.,ult. 2 fuel, pro circuit pipe and 304 silencer, 12/51 gearing and timing advanced.also i asked eric for te mo-better porting.
it sounds like that will be a fun bike! the jetting can get a bit wacky, if you are having problems with it being too rich you might want to try the stock reeds again as that is where my rm had the problems, but i doubt that will happen if you are running the U2. just pay close attention to pinging and maybe do a couple of plug chops to get it tuned real close. :thumb:

i race vet class on my rm144, i love the bike but starts are the worst- there is nothing worse than watching a bunch of 450's disappear into the distance- i usually do ok with starts on my 250- but its all bout the rider, ive not been competing that long, a guy on this site that shall remain nameless rides expert and often holeshot against 450fs on his 03kx133 :worship:
 

marcusgunby

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#3
LOL bruce, angus the 144 kit will make your bike faster, but it wont suddenly shave seconds off you lap times, it may give you a better start against the big bikes but starting is mostly technique just like riding, i would say get the big bore , but dont expect it to make you win races.
 
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#4
i hear what your saying that it is 95%rider and 5% bike and believe me trying to get the most out of kawasaki is not easy. i'm just looking for alittle help once i get out of the gate. once out of the gate it's fairly even then as we pick up speed and go through 2nd and 3rd gear the blue train seems to pull away. part of the problem is mine is a 6 speed and yamaha's are 5 so they can pull through each gear longer. So hopefully with a big bore kit and proper gearing now maybe I can compete. Like I said before I don't mind working through the pack but hopefully this will help so I don't have to spend as much time working through the pack to get where I want to be. Also if you could please answer the jetting question. How many main jets and pilot jets did you have to drop? And where did you see the power after you installed the big bore kit and what porting did you ask for? Once again thanks for any info.
 

bclapham

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angus, i dont know what the gearbox is like on your kx, but on the rm, i start in second and by the time i am getting good traction i will have the throttle pinned to the stops and i then just fire through the gears- no clutch, no letting off on the trottle- it stays pinned open! i cant do that on my yz250, it wont shift without backing the thottle of a little

dont forget, good tires in good condition and at the right pressure are real important, as is getting right on top of the gas capwhilst on the line- at least that helps me, but i am tall!:)

dont know about your jetting, so many things change, you just cant predict it really and you will just have to experiment a little- what carb is on that bike btw? and what size?