Question about 2003 Yamaha YZ 125

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Why would my 01 yz 125 flood out i just put a third new top end on and it floods out and the piston goes bad

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Have you made any airbox or exhaust modifications? (too oily air filter, clogged chamber, dented header)
Are you running stock carby/jets? Using the correct range sparkplug?
Check condition of reeds, they may have relaxed their tension and are remaining open, or been damaged by carbon blowback.
Are you using the right fuel at the correct ratio?
Are your crank seals in good condition (is there any sign of fuel oil weeping from behind magneto?
Are the conrod and crank pins okay? (excessive piston side play or up down freeplay)
Is your ignition providing a healthy spark? (coil condition and good earth)
All these issues can have a bearing on your problem, goodluck.

Posted on Nov 12, 2010


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Hi, Jason and the usual suspects are:
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2004 yamaha yz 125,All stock,wont kick start but will pull start,then it sounds flooded and gas smell is real strong.wont idle withoutkeeping motor reved.thanks forthe help......

sounds to me like the carb needs sorting, either the float height needs setting or the needle valve is leaking. to test if it is either of them try turning the fuel off and start it, if it runs a lot better then thats your prob.

Mar 14, 2011 | 2004 Yamaha YZ 125

1 Answer

I have a 2000 yz 125. Melted a hole in the piston but didnt score cylinder. Replaced top end. Wont start. Has good fire. Crank case oil was a little grey. New plug,fluids,fuel.

I would be checking compression it may not be visible score on cylinder but it does not take much to loose compression on small bore motor with one piston ring and 11 years old

Mar 03, 2011 | 2003 Yamaha YZ 125

1 Answer

What color piston does a stock 2004 yz 125 come with?? Im rebuilding my top end but theres different color oem pistons? whats the difference???

Hi, Mezacarlos for this situation I would call my local dealer or reputable shop's service/parts department and inquire about any possible quick fix, answers, or parts inquiry. For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
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Dec 18, 2010 | 2004 Yamaha YZ 125

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When i crank my bike it runs but when i hit the gas it bogs down and dies nless i let off of it. why does it do that?

my 03 yz125 does the exact same thing... its driving me insane... i got a new spark plug for it and that still didnt fix it.. i dont know why its doin that.. i think it needs a bottom end rebuild, which is retarted coz i already forked out to pay for a rebuild not long ago

Sep 18, 2010 | 2003 Yamaha YZ 125

1 Answer

Tons of smoke coming out of exhaust

A bad crank seal on the right side, if bad, will **** transmission oil into the combustion chamber. This will smoke badly.

Jul 16, 2010 | 2003 Yamaha YZ 125

1 Answer

How do I remove the piston from my 2003 YZ 125?

Hi, Jakephair for this scenario you will need your service/owners manual if you can't find the first and best tool you ever bought for your Yamaha, despair not, for a mere $0 you can download another one. For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a nice day.
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May 19, 2010 | 2003 Yamaha YZ 125

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