1999 kx 125 hesitation right before powerband? help!

john stu

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#1
this is for the experts a friend of mine has a 99 kx125 that is basicaly stock with stock jetting at sea level. the bike has good bottom for a 125 and good top for a 125 but just as the bike is about to hit powerband it loses power for a second or two and then goes into powerband and pulls fine all the way up. the bike runs storng off idle its just a small rpm range right before powerband that is the problem it doesn't compleatly bog out it just loses its power and lind of gurgles a little. the bike has a fresh top end, resent crank and when doing the top end the powervales operated very smoothly and seemed to have little carbon i tried moving the needle clip up and down one clip with no luck also tried one smaller size main and one bigger main but the bike runs best with the stock sizes i am thinking maybe something is wrong with the power jet but how to i check this? or does anybody else have any ideas? he doesn't have a lot of cash so i don't want to just start replacing parts unless i am sure it will make his bike run better. it really feels like there is a rich spot in the carberation right at that rpm would a bad power jet do this?
 

IrishEKU

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#2
I would say clean the carb, check the jetting and drive on.

An easy fix would be look for a bind in the throttle cable. Being as new as it is I doubt it's that.

Flush that Carb.

Good Luck,
 

john stu

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#5
jboomer i was just trying to help a friend out, or have you never done that before? i was looking for some sugestions like matt h posted. thanks mat i will keep that in mind
 
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#6
Just a little more on what I already posted. I believe I went 3-4 sizes smaller on the power jet, if I still had it I'd chech but if it does you any good I "think" it was a 38.
 
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#8
Ya it did but after a full day of testing stuff out like jets, oil, and fuel. I found I had to run a fully snythic oil at 40:1 ratio race fuel cleared it up but couldn't afford it. so ended up using Torco GP7 40:1 with 91 octane and leaned my jets abit just play with it you'll find it eventaully.
 

Big Daddy

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#9
Try using the choke to determine if its a lean or rich problem while driving. Mark your thottle at four spots to see in what area the problem is. 1/4, 1/2,3/4,full. You might be surprised to see were the problem is. I had the same problem and went to a richer needle that had a steeper taper to fatten up 1/2 to 3/4 thottle. 98cr125
 
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OKKX'er

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#11
Check your ignition timing. I have seen timing that was retarded in search of more overrev cause what you're feeling.
 

john stu

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#12
no the top end power is fine once it get on the pipe but thats a good idea i think i will look at the timing anyway like i said i cant do anything now i have to wait till spring
 
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CaptainObvious

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#13
John,

I'm resurrecting this old thread to see if the power jet was in fact your problem. My bike is jetted correctly in the pilot, main & needle, but I too have that hesitation right before it comes on the pipe.

I really don't know what the heck the power jet does or how it interacts with the other circuits.