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2003 YZ125: Carb Overflow Hose Is Leaking

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My son's 2003 YZ125 leaks fuel out of the carb overflow hose at idle, and near-idle rpms. It also continues leaking after the engine is shut off. Once the fuel petcock is turned off, it stops leaking after a few seconds .

I'm not sure if this is likely due to the float needing adjusting or not. It hasn't been ridden much in the last few years, but it never leaked prior to that period of inactivity.

Thanks,

Terry

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Its either the float sticking or the float level is set to high. If its set too high you need to bend the tang that the needle valve rides on down. Had this issue on my 250 this spring.

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Sitting often causes the float to stick.

Try tapping on the float bowl with the wooden handle of a hammer or with a rubber mallet.

If that doesn't work you'll have to disassemble and and rebuild the float seal.

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Take the carb apart & clean the float needle and seat. I use pipe cleaners to get in the needle seats. Might aswell clean your jets while your at it.

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Sounds like you have some junk in your carb. Try turning petcock off, then run it till it shuts off. Sometimes that will fix it, if not remove and clean needle valve

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Thank you all very much for the suggestions. I've jetted a few Kehins on KTM 300's, but I never had to remove them. This YZ125 has a Mikuni which I've never messed with before. The bike has seen very little riding in the last 4 years, but it's running very good, just has the overflow leak. Are they fairly easy to remove without getting all the hoses confused?

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Yah, you'll be able to tell where each vent hose is supposed to guy. If your really worried about it, take a few pics before you get started. Remove the bowl and the jets, give everything a good douche with carb cleaner, and blow it all out with compressed air. Should be good to go

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before you take it apart get it started let it idle and spray short bursts of carb cleaner into your intake that may help.

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before you take it apart get it started let it idle and spray short bursts of carb cleaner into your intake that may help.

If you do this you run the risk of removing the oil coating off the intake side of the piston. Not a wise thing to do on a 2 stroke.

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i do not do very much , nothing liberal at all, also it is even what the can of carb cleaner says to do. even for two strokes.

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if it never did that before replace the float needle and seat. i have seen a lot of them go bad from sitting for a long time. they get a little ring around the rubber tip and won't allow the gas to stop flowing when the bowl is full. 

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First, I would order the float needle and seat. They are cheap and they dry out and go bad when a bike has been sitting for a few months. Once you get the parts, in take apart the carb. Clean the carb out, replace the float needle and seat, and double check the float height. You wont have any problems with the overflow after that...

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I have an 03 yz125 with an overflow leak problem, or rather, had. I replaced my float valve and seat, still didn't help, replaced floats, problem fixed. Guessing the floats were saturated. Try replacing the floats, don't waste time and money on a float valve kit. Hope that fixes it

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Also mine has the stock mikuni tmx38 flat side (slide or side?) carb. That's what yours should have if everything is stock

This thread is a few years old, and the bike has the TMXx 38mm round slide stock.

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This thread is a few years old, and the bike has the TMXx 38mm round slide stock.

I'm pretty sure that's what I have on mine... If I'm wrong thank you for correcting me

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Likely you need the oring on the needle valve seat.  The rubber tip needle valve itself may also have hardened or gotten a horizontal groove from sitting against the valve seat.

http://www.rockymountainatvmc.com/oem-schematic/0#  Number 11 under "carburetor" is what you likely need.

 

http://www.thumpertalk.com/topic/1079107-2001-yz-125-carburetor-overflow-leaking/?hl=%2Boverflow#entry11514980

 

http://www.yamahapartshouse.com/oemparts/a/yam/50044d3af8700209bc791207/carburetor

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On 7/29/2013 at 5:14 PM, Elrod1529 said:

Its either the float sticking or the float level is set to high. If its set too high you need to bend the tang that the needle valve rides on down. Had this issue on my 250 this spring.

After seeing this and doing this fix. It will be the last thing you’ve checked if you still have a problem after reading the bss comments on forums on carb leaking

everyone says all the shit about carb leaking but a lot of it could be Something as easy as the two pins from the float yet connected to the flow tab need to be tightened.  Saying it might have just play between them. That’s what was the problem on my yz 125 2005 for 3 years. Even when I tilted the bike it do it then straight up it wouldn’t but it got worse. 

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