04 YZ 125 idle low and running way rich

Hi Gents, New to this part of the forum. I recently purchased a 04 YZ 125 and am having issues with getting the bike running right specifically on the low side. I ride mostly at 5500-6000ft, with an average temp of 25C/77F. The bike idles but very slow, I can turn the idle screw in all the way or even completely out all the way and it makes no difference. What's even more confusing is you can turn the air screw in all the way and out all the way and it makes no difference either.

So I pulled the carb cleaned it thoroughly even put it in a hot chemical bath for a while the carb came out shining. Replaced the needle and seat, set the float height and started changing jets. I'm eventually down at a 20 pilot and still no change. The plug is still wet although a bit better than before.

Iv replaced the intake boot, sprayed carb cleaner every where with no change. Iv pulled the air filter off to try and lean it out even further no difference.

Next step was to check timing. Initially I advanced the timing off the bat and it seemed to make a difference, I could adjust idle but not for long it would just slow down again. So pulled the magneto to check the key it's perfect no problems there. So adjusted the timing according to the Manual. .02" BTDC marks lined up perfect. Ran the bike and still the same as before no matter what I do with the idle screw or even air screw there is no change.

If anyone has some advice on what I should try next it would be greatly appreciated.

Check that the idle screw is physically engaging the slide when turned.

Remove the air screw completely to see if it is damaged somehow. I think yours should have a "truncated cone" tip shape. Clean the passage behind the air screw with some fishing line.

Hi, thanks for your input. I done exactly that, still no change! Called up a mate with a 2010 Yz and asked to trouble shoot with his carb!! It works great could adjust the idle and airscrew with noticeable difference With his carb, I then changed to my slide, had no issues, changed his idle screw with mine no issues, changed his air screw with mine no issues... It basically leaves me only left with the carb body, so I pulled it again used some guitar wire and cleaned all the little holes!! Still no luck!! I'm stumped!

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