Question about Yamaha YZ 125 Motorcycles

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A lot of gas coming out of the carb. overflow tube, eng on or off

When the fuel is turned on gas starts coming out of the overflow tube. It doesn't matter if the engine is running or not. The bike will start and run like there is nothing wrong. But, the gas is dripping severly out of that tube. The bike is a 2001 Yamaha YZ 125, we bought it used about 5 months ago and have no idea how many hours are on it. I used to work on minor things on my own dirt bikes but that was over 20 years ago. This is my son's bike and I'm hoping it's something I can fix. Thanks for your help.

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  • Anonymous Mar 30, 2014

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  • Master
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The float pin is stuck or has some dirt in it. try tapping the side of the float bowl(s) with the handle of a screwdriver... not hard enough to break it. if that doesn't work you will likely have to take the carb apart and clean it.

Posted on Apr 06, 2009

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6ya6ya

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SOURCE:

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Posted on Jan 02, 2017

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tombones

  • 3567 Answers

SOURCE: yamaha yz 125 1994

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Can I get a “very helpful” rating on this answer? Thanks!

Posted on Jul 06, 2009

tombones

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SOURCE: how do i decode yamaha yz 125 engin id number

You don't decode it. It is only a production run series number. Mororcycles are like cars in that respect. It is the frame number, AKA the "VIN number", is what carries all the information. Call a dealer with the frame number and he can tell you year, paint color, specific model and more. They may have a problem if the bike is too old. Yamaha changed to a newer code system a few years back.
Can I get a “very helpful” rating on this answer?

Posted on Aug 28, 2009

tombones

  • 3567 Answers

SOURCE: I have a 95 yz 125 head and 98 yz 125 bottom end.

You have a 50/50 chance that they will work okay. All the mounting holes need to line up and the cooling holes as well. Get a head gasket for the '98 and see if all lines up. Will the exhaust pipe fit the '95?

Posted on Apr 30, 2009

mxtras

mxtras

  • 194 Answers

SOURCE: 2008 yamaha yz 125 carburator

You say it's flooding - is fuel coming out the overflows? If so, you might need to replace the needle and seat, but based on the age of the bike, I wouldn't think you would have to do that yet. Even with a bike that is raced, you can get many, many years on the needle without having to replace it - unless something damaged it. Inspect the needle and seat closely for nicks or imbedded **** in the sealing area. Also - I assume you set the float properly. This is an important step. Personally - I think the factory setting is too high - since about 2001 I have set the float 2MM lower than recommended. Otherwise you will have fuel pouring from the overflows on the faces of jumps or in the whoops.

If the engine is "flooding" - it could be down on compression which will make it run rich. Or you might just have to re-jet but I would only re-jet if the engine is fresh. You can also try running a B8ES pluf - it's a step hotte than stock and what I ran. Keep in mind that the ring in a 125 doesn't last long at all. There's only one ring. I would replace the ring before each race when I was running 125s - this happened every week during the season. 2-3 ring replacements per piston, 4-6 piston replacements per cylinder.

If you provide more info, I can give you a better answer on your exact problem - I don't know if I really know exactly what the problem is.

Scott

Posted on May 20, 2011

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Hi, Anonymous and the usual suspects are:
1. Damaged or restricted fuel tank venting system.
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I think your talking about an Overflow gas tube that keeps your enging from flooding from too much gas, your carb may need a little adjustment so you stop dumping gas.

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Start trouble shooting through these. Make sure your gas is turned on, and that it flows through the carb; if you tilt the bike does fuel run through the overflow tube in the carb? Make sure you have good spark; take out the spark plug from the cylinder, still connected to the ignition wire touch the threaded end to somewhere metal on the engine and turn the bike over. You should see a spark. Finally, do you have good compression, how hard is it to kick over etc.

These are the first things to trouble shoot, I would look on youtube if you don't know what you're doing, there are plenty of helpful videos there. You can also try putting a thimble full of fuel into the cylinder and then kick it over to help it start if it has been sitting a while.

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