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My KX125 keeps fouling plugs.

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I recently bought a 05 kx125 and took it to the trails for the first time last weekend. I rebuilt the top end the week before and it runs great. After our first round through the trails we stopped for a water break and then my buddy wanted to take it for a spin. He took off and as soon as he shifted to second it loses power and dies, so we pop in a fresh plug and it runs again. The next day I'm messing around in a field with it and it does the same thing again. Has anyone else had this issue? Any good advice will be very appreciated.

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lean the jets. or yo may possibly have a leaking head after the rebuild. Did you by chance true the surface of the head?

03-05 125's are jetted extremely rich, stock. When I first got my sons 03, it would foul the plug as soon as you lugged it around and not on the pipe.

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I took the easy way out, my 99 would do the exact same thing. I couldn't even get 10 minutes before it would foul. I switched to a hotter plug, 9 to an 8. I haven't fouled a plug since early summer, wether I lug it a bit or not. Keep us posted.

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Thanks guys. Sappers, I didn't bother checking the head. This bike has real low hours and ran great when I bought it recently. I'm almost sure it's due to lugging it a bit. I know 2 strokes like it on the pipe but I find it impossible to do this always, of course, I am a newbie! I will keep you all posted as soon as i find something out.

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On my -07 kx 125 the original jetting is way too rich.

I run a #370 main and a #35 pilot.

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On my -07 kx 125 the original jetting is way too rich.

I run a #370 main and a #35 pilot.

thats what I have in ours & clip on top notch. took the sputter out and hits hard.

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I took the easy way out, my 99 would do the exact same thing. I couldn't even get 10 minutes before it would foul. I switched to a hotter plug, 9 to an 8. I haven't fouled a plug since early summer, wether I lug it a bit or not. Keep us posted.

Oddly enough I just happened to have had a hotter plug so I put it in. I'm two rides in and no problems. Thanks

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fixing the fouling issue doesnt actually fix the problem, all you will do in time is clog the KIPS and make your exhaust a mess. you need to rejet, and plus it will give you more power and will just run better.

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the 05 I just picked up seems to want to load up pretty quickly just putting around my parking lot. I'm riding some somewhat fast/wide trails tonight and was going to drop in a 380? Honda dealer is going to rape me $10 for a jet most likely so I just want to lean it out a little for now.

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