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Upbasher

YZ125 bogging on low end

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Hey guys I have a mint shape 03 yz125, its all stock. The bike has tons of top end power, more than enough, but on low end it has nothing.

When you take off on it, it bogs badly and then all of a sudden perks up and gets tons of power. I have read and heard that this is normal, but it seems particularly excessive. When I'm in sand I can barely start at all.

My friend told me it could be that a jet is plugged in the carb. Could this be the problem? If not is it supposed to be like that or is something wrong?

If it helps any, I weigh exactly almost exactly 180 pounds

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I just got done with this problem in my carb. First off clean your carb. Pay attention to the pilot jet especially. Make sure nothing is built up in it.

After that if it's still not running good, you need to change your pilot jet. Cooler weather will make your bike run leaner so switch to a larger pilot jet to make your bottom end richer.

Changing the clip on your needle can also richen the mixture. If you look at the needle with the notched end pointing up and the needle point pointed down, moving the clip down one notch will make the your bike richer.

In my case my bike was terribly jetted when I got it and I actually had to lean the bike out alot, even with cooler weather.

So first just try cleaning your carb, then if that doesn't work try adjusting your needle and if that doesn't work get a bigger pilot jet

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How fresh is the motor (hours on top end) or better yet how much compression does it have? Pump gas is awful when left in carb more than a few days, take apart and clean and look for corrosion or pitting (usually behind a white residue). Probably the pilot jet clogged though.

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On 9/29/2013 at 1:13 PM, tribalbc said:

I'd put money on your powervalve being stuck open.

Haha i know you posted this a long time ago but I’ve been having the same problem on my bike right after i rebuilt it so i was thinking it was a power valve problem too. What should I do?

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Just now, Rosehill Ryder said:

Or broken . Our 2005  broke and so did our 2014 . 

what qualfies them as broken? because mine are a little chewed up at the end but not bad 

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1 hour ago, Thomas Garmoe said:

what qualfies them as broken? because mine are a little chewed up at the end but not bad 

Ours were broken in half . When manually trying to operate the powervalve only one side would work . You can take off the exhaust and look into the cylinder to see if it's operating . You will need to remove the powervalve arm cover 1st . As has been said by others this may not be the cause , but this does not take that long to check .   I can do this check in 5-10 minutes . But , I'm very familiar with doing this . By checking it this will be one cause eliminated . Good Luck .

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