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YZ 250 jetting / idle / running problem

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HI guys,   my yz is badass but has a problem I have never had with any of my previous yz's of the past,

 

In neutral, blipping throttle, bike hangs, then settles briefly before it dies.  If I raise the idle, it hangs pretty fast, and idles too fast but it wont die.

 

I am after a smooth throttle response for difficult terrain.   riding in Hawaii so its hot and humid   sea level up to about 1500.

 

38mm keihin, jd blue #3, 48 pilot, 160 main, #8 slide.    this is pretty good riding but the bike wont idle like I said above, something is wrong.

 

I tried to check all seals, potential air leak spots, but nothing is obvious.   a friend mentioned wd40 to check leaks, but where do I spray?

 

pipe is sealed with silicone gasket maker and good orings,   a 50 pilot didn't fix it(bike feels a bit stronger maybe), the needle in clip 4 didn't really help either.   a few other needles were tried but the results are worse than the jd blue that came with the bike.   Do I need to go much richer still from stock to fix the idle problem?

 

I tried a 36mm lectron, and I don't remember it idling funky like this.   it did however have much too abrupt power delivery with the 3-2xl rod so I took it off.   I may try again in the future with a different rod,  david said to try the 2-3 rod for better results. 

 

is it possible the bike runs worse with a 13' stock can with fresh packing?   I traded my r304 to get this silencer and I am bummed as its the only thing I changed and the bike seems a little worse now.    at this point I still think I have an air leak but I don't know how to find it.

 

help much appreciated thanks!

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Did you try turning your air screw in and re-setting idle? I would assume so.

Probably have an air leak. Build a test rig that pressurizes the cylinder and crank seals. You will likely learn nothing from spraying wd or starting fluid on things. There are threads here that describe it. 20 bucks worth of parts from home depot does the trick.

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air screw and idle were always around 1 to 2 turns.   the idle screw is turned pretty far in but there is still some room before it bottoms out.

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So I built the tool, and did an air leak test to find the bottom end will hold 10 psi for what has been 20 minutes now.

 

at first the bubbles revealed a small link on the right side pv  cover plate area.  but that went away for some reason.

 

 

does this mean, perhaps the air boot is suspect? or maybe the air filter?   If this forum didn't exist I would probably rebuild the carb at this point.

 

 

thanks  for any help

Edited by shaheeb

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