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Help with big bore/elevation jetting

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Ok so I have an 06 kx250f with a cylinder works 269 big bore kit.

I have a full pro circuit exhaust system

I live at 5800 feet elevation

I cannot seem to get the jetting right for this setup.

any ideas or where to begin

thanks

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carb is clean. it is very hard to start,

the other issue is it just drops off at high rpms, basically stops pulling.

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Did you ever figure out the jetting on your bike?

I am having the same problem on my bike I live in 5500 or so and from half to full throttle it cuts out

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not yet. I actually have taken the head of for porting and polishing and new valves. I am getting it back this thursday. After that I will try to dial it in. I will post my findings after that

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I have a 2008 kx 250f with a 290 vertex big bore and stage 2 cams.. Cams make no difference.. I didn't change my jetting when I went to the stage 2 hot cams.

Stock jetting is 182 main with 42 pilot jet.

I went with The JD jet kit with the red needle in 5th position on the clip, 178 main, an adjustable leak jet. I also went to the JD fuel screw as well. My bike ran excellent from the start. My elevation is 3500 ft. When I pull my spark plug out it looks like brand new!.. Perfect!.. Runs cool.

In your manual you will find that it has great jetting recomendations for elevation. Check the chart out.

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You shouldn't be far off my setup.. you won't need to change the pilot from stock. I would definitely go to the adjustable leak.. It will solve any acceleration problems.. Just keep adding fuel until it doesn't increase your acceleration! With your elevation you might be a 175 main.. but remember if you run the red needle with the JD Jet kit.. it's a fatter needle.. which means that it tends to be leaner.. Run the bike up a hill in 2nd gear at 3/4 throttle and shut it off.. Coast down the hill and check the plug.. this is your main jet. My plug was white on the ground strap with a 175 main meaning the cylinder temp was higher.. I could run a 175 main but it would be a tad lean... The 178 was clean as a whistle. JD recomends a starting point of 180 main.. Your increase in cc's means the motor pulls more air and fuel through.. that means the bigger bore generally runs a leaner setup.

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