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kx80 sputtering topend

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jabbahoo:
My sons 87 kx80 has a problem with sputtering and missing real bad on topend. I checked the carb and its clean. I checked the muffler its fine and I checked the cdi. It ran fine this summer but when the temps changed from upper 90's to low 50's it now runs like crab on topend. Could this be caused just from jetting? I'm new to the 2 strokes and just wondering what I could look for? The bike is all stock with a 200 main jet. Should I try and go leaner or richer on the needle? any advise will be greatly appreciated.

r1ray:
Definitely sounds like a jetting issue.

jabbahoo:
So should I lean it out or richin up the needle? Which would cause the sputtering?

FuriouSly:
The main jets for that stock bike are 170,180,190,200,210.  Would be safe to go down one at a time from 200.  Not knowing the condition of the bike and motor, hard to tell what you got going on.  Elevation, temp, humidity all effect jetting.

Going leaner on the needle is different than going leaner on the main.  Your terminology is a bit off. 

The main is in control of the top-end and overall fule flow off on idle.

The pilot jet runs the idle up to 1/4 throttle and a smaller effect up to 1/2 throttle.

Then the needle height effects the midrange throttle response.  Dropping the needle down into the main jet leans out the fuel (raising the clip up the needle) and crisps up throttle response.

Have to get the float height and main jet dead on to get the needle set.

Sly

John:
Hi,

Is this the first time the bike is causing you trouble? How long have you had it? Is the bike new? Has it worked fine before?

It would help to understand the problem if you could give a bit of history...

//John

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