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Discussion Starter · #1 ·
got this bike it says by the frame that it is a 125sx but the jug on the bike is a 200cc anyway the problem that i am having is that after a top end rebuild new cyclinder and bore and piston rings runs great but will not make any power at take off will not even pull the frount tire off the ground. about 3/4 through the 2nd gear at the very end it willl start the make some power but after you goto 3rd samething again running but on really makeing power till you really wiend it out at the top of the gear other than that the bike runs just not at what i think it should be like. my thinking is that should have trouble keep the frount down on the ground. what could cause such problems ? any ideas anyone thanks in advance for any help
 

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my kx 125 didnt make any power down low and from what ive heard 125s dont really make power till you winde them out.
 

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Thats a small cc engine for you. They like high rpms to get the bike moving. But also check to make sure the p/v is working correctly and bottom jetting is workable.
 

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Their should be some punch to it. Start simple and check the pilot jet and air screw settings and then the powervalve and make sure it isn't sticking open.
 

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Discussion Starter · #6 ·
when you say power valve you are talking about the valve in the exhaust port like a flap that opens and closes with the engine pulse ? if you are yes I did have some problems with that clearing freely after i got the head back from the machine shop but i did do some grinding on the port so that is would move freely before in stall. looking at the little window on the side of the head it looks to me it is working and in time as per the book Thanks again for all the help
 

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If everything else is good it might be the stator starting to go.
 

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you said you had it bored is the bore size to spec with the piston and vice verse?? i have a stock 125sx that i have rebuilt a couple of times with all the low end i need it is true that the smaller cc bikes love the R's but they can still provide a considerable amount of low end power. Also how old is your pipe and silencer check to see if cracked or clogged is the pipe smashed or have big dents in it?? being a two stroke the shape and volume of your expansion chamber drastically changes the performance of your bike.
 

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Im not a KTM guy, but there is not a SX version of the 200cc, its going to be a EXC or XC/W.
Can you verify the serial on the bottom end?
 
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