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  #1  
Old 07-30-2004, 06:47 AM
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Default THIRD TIME

I had been posting previously. Look at "Leakdown Test"
'02 YZ125. Wristpin sides of piston melted. Electrode on plug melted. 1st full tilt run after top end rebuild, same thing. Checked everything I could think of. Leakdown test, good, sprayed starting fluid all over motor, no rpm rise, changed crank seals anyway, had carb checked out and cleaned, checked timing, dial indicator and everything. checked reeds, good water flow, new gas mix, B8ES plug. Only thing I have left is power valve. Checked for free movement and linkage, everything looked good.
Anybody know if PV malfunction can cause an extremely lean condition. I don't think so but I'm at wits end.
Sorry for the long post, think I need counselling. This makes the third time it has melted!
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  #2  
Old 07-30-2004, 06:59 AM
Aus_Rider_22's Avatar
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Default Re: THIRD TIME

There are a few different things to look at.

May I ask how you warm your bike up? And for how long?

Check here also: http://www.eric-gorr.com/twostktech/...aguide_2t.html
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Old 07-30-2004, 07:14 AM
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Default Re: THIRD TIME

I'm going through nearly the same issue with one of my snowmobiles.

I have $600 into a motor that has moved 50 miles in 3 years.

I feel for you.
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Old 07-30-2004, 07:32 AM
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Default Re: THIRD TIME

The bike is always at operating temp, B4 we go enough throttle to get into the pipe. At least 3 or 4 minutes of slow riding. The first time this happened, my kid was riding for at least 20 minutes, then full throttle on straight, melted. Second time was after top end rebuild. Broke it in, by the book. Ran fine. First wide open run, up to 3rd gear. Melted. Went through all the checks and measures, cleaned up the piston, (probably not recommended, buy didn't want to destroy a new piston,just in case). Put bike together, slow riding to check everything out. Screamed it a little. Melted. Bike is completely stock. Jets and all. We bought it used. We rode it 4 months B4 the first melt. Changed nothing.
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Old 07-30-2004, 07:37 AM
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Default Re: THIRD TIME

That seems to point at cooling maybe. Have you checked all radiator hoses for kinks and make sure there are NO blockages.
Also make sure radiator isn't blocked up with grass or foreign debris as this stops air rushing through and cooling coolant and engine.

Last edited by Aus_Rider_22; 07-30-2004 at 07:40 AM.
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  #6  
Old 07-30-2004, 08:12 AM
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Default Re: THIRD TIME

Water circulation, eveything looks good. warms up pretty fast though. This wouldn't have caused the plug to melt. Has to be an extremely lean condition at full throttle, to melt steel.
I'm baffled!
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Old 07-30-2004, 10:43 AM
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Default Re: THIRD TIME

It might not be the cause, but how is your left side crank seal?
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  #8  
Old 07-30-2004, 10:46 AM
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Default Re: THIRD TIME

I took the left sidecover off, sprayed starting fluid all around with the motor running. No rpm rise.
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  #9  
Old 07-30-2004, 10:54 AM
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Default Re: THIRD TIME

your main jet isn't clogged with something is it??
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  #10  
Old 07-30-2004, 11:26 AM
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Default Re: THIRD TIME

Had the carb cleaned and jets checked between 2nd and 3rd disaster. All stock jets, checked the numbers. Air screw 1 1/4 turns out. Didn't change jets or any settings, from when we got the bike. Rode it fast and hard for 3 months B4 anything happened. I was actually getting ready to rebuild the top end, when it blew the first time. Figured it was about ready. Guy rebuilt top right B4 we bought it.
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