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yz426guy619

fuel leaking from bottom of carb when fuel is "on"

31 posts in this topic

Hey all. I have a '02 YZ426 and it has ran perfect for the past year. I was out in the desert last weekend and I noticed whenever my fuel valve was turned in the on position, fuel consantly drips out of the tube coming out of the bottom of the carb. The bike still runs good while the carb is spitting out fuel :thumbsup:. Any help would be appreciated. Thanks for your time.

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There are 4 possible things:

The o-ring on the little tube thing that the float valve sits in is worn.

The float valve is worn.

There is trash on the float valve preventing it from seating.

Your float height is set wrong.

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Usually turning off the gas and beating the carb with something will clear the speck that is keeping your needle from closing fully.

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Funny, my 02 YZ426 started doing the same thing this weekend. Sadly, I kept forgetting to turn the fuel back on before taking off again.

Oh, and I forgot my boots at home, so I was wear tennis shoes.

My foot is still bruised from kicking it over so much. :smirk:

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My 01 YZ250F was leaking gas out of carb tube and I replaced the needle and seat to correct the problem.

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The Breeze covered all bases.

especially the leaking seat that the float needle sits in. Hope that isnt the case if its a pressed in seat and not a removable one:banghead:

I think the 426 had a removable one though. Why they went to the pressed in ones is beyond me...So they could sell you a 1000 dollar carb? I would get a new needle and seat assy.

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Since the needle seat O-ring is cheap and available separately from Yamaha , I would replace the O-ring first. This same scenario has happened in the FCR carbs of several of my friend's KTM's.

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The seat itself rarely goes bad. They started pressing the seats in in '03, so the '02 should still be replaceable. But then, on the replaceable ones, you have to buy both the seat and the needle anyway. The screw-in seat has an O-ring on it that can fail. The tip of the needle can dry out and crack if it is an older unit that sat dry for too long.

Sometimes you can drain the bowl, turn the fuel on with the drain open and wash away a piece of debris. Draining the bowl lets the float drop far enough that the needle isn't trying to trap the dirt against the seat.

Sometimes a shrunken O-ring will swell back up and seal.

But sometimes you just gotta replace it.

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Thanks guys. Is it something that a newbie to bike maintenance like myself could perform with the manual or should I take it somewhere to get the work done in your opinion?

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You can do it yourself for sure, dont be afraid to take apart your bike. Youve always got your manual and the guys on here in case something happens. Just take your time, and be patient.

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Thanks guys. Is it something that a newbie to bike maintenance like myself could perform with the manual or should I take it somewhere to get the work done in your opinion?

IMO you dont even need a manual. all you have to do is loosen the carb clamps, turn it sideways, loosen the 4 screws holding the float bowl on, and clean everyting inside

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IMO you dont even need a manual. all you have to do is loosen the carb clamps, turn it sideways, loosen the 4 screws holding the float bowl on, and clean everyting inside
Sounds like a great place to live.

According to Murphy, with the bowl sideways he'll take it off, the float pin will fall out, dropping the float on the ground, and the needle will go...somewhere. :smirk:

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Sounds like a great place to live.

According to Murphy, with the bowl sideways he'll take it off, the float pin will fall out, dropping the float on the ground, and the needle will go...somewhere. :smirk:

the pin shouldnt fall out

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Having the exact same problem with 06 YZ450F :/ Why are all the bike shops within 100 miles of me closed Sun/Mon?!?! grrrr...

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Having the exact same problem with 06 YZ450F :/ Why are all the bike shops within 100 miles of me closed Sun/Mon?!?! grrrr...

bike shops will prolly charge you $100 to do a 10 minute carb job

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