Question about 2003 Yamaha WR 250 F

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I have a Yamaha 1995 wr 250z. I have replaced the piston in it twice now, it keeps melting before I can even break it in. I bought it blown up, and put a sleeve in it and put it together myself, this time I've had a mechanic go through it and put it together and before the mechanic could break it in the piston has started to melt again. we've adjusted the everything you could think of that would deal with it getting hot. Got a new carb boot, adjusted the fuel...... does any one else have this problem, and why does it keep happening?

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  • Yamaha Master
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Hi, William_s83 ouch!!!! I feel your pain you may have what is called "PRE-IGNITION" and the usual suspects are:
1. Spark plug heat range too high.
2. Spark plug loose in the cylinder head.
3. Broken spark plug porcelain with carbon buildup.
4. Foreign particle embedded in the combustion chamber.
5. Excessive carbon deposits on the piston head or in the combustion chamber.
6. Points ignition timing too far advanced due to improper timing plate position.
7. Faulty electronic ignition sensor inputs from the MAP, CKP, CMP to ICM/ECM.
8. Engine overheating due to lack of lubrication or coolant.
For more information about your issue and valuable "FREE" downloads that you will need please click on the blue links below. Good luck and have a wonderful day.
keeps melting pistons
How to Break in New Top End EnduroNut Method
YAMAHA WR250F Owner Service Manual
OEM parts for Yamaha
Yamaha WR250XZ Owner Manual

Posted on May 08, 2017

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  • Yamaha Master
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Using the wrong grade of fuel can cause that. Octane too low causing pre ignition.

Posted on May 08, 2017

6 Suggested Answers

6ya6ya
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Posted on Jan 02, 2017

  • 2336 Answers

SOURCE: yamaha FZ 750 FM

It sounds like the idle screw is not set right., but if your going to clean the carbs anywyas. Clean them, sync them and see how she runs, if still doing the same thing the idle screw needs to be adjusted. The RPMs should be between 800 to 1200 while idling. If your bike is an older on it will most likely sit around the 1200 rpm at idle.

Posted on Nov 10, 2008

  • 82 Answers

SOURCE: hi i have a 1998 yamaha yz 250 that when you start

Are you loosing transmission gear oil? I seem to remember an older bike I had with a crank seal issue. Gummed up plug is usually only 2 things:
1) Carb too rich. Check jetting or sticky float needle valve that will dump fuel into the intake manifold.
2) Too much oil (check mixture ratio or crank seals that is mixing crankcase oil with the fuel mixture). Either of these two oil issues should produce a massive amount of tailpipe smoking and a noticable drop in power.

Posted on Apr 29, 2009

  • 200 Answers

SOURCE: Yamaha Fazer 600 - keeps breaking against me when riding

I suspect poor fuel delivery or starvation. At those rpms your bike requires a lot of fuel.Replace any and all fuel filters, check fuel lines for any kinks. Drain tank (petcock on pri ) then remove and clean petcock , replace. Run a bottle of techroline thru your next couple tanks of gas....Good Luck to you my friend...Tim

Posted on May 10, 2009

  • 208 Answers

SOURCE: 1998 yamaha grizzly engine noise

you may have a collapsed lifter

Posted on Jun 21, 2009

SOURCE: my fzr 600 keeps blowing the main fuse, if i try

Check your battery cables to see if you have direct short. that is what it sounds like.

Posted on Aug 22, 2009

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I was recently riding down and enduro trail when i laied my 2003 WR-250F over and when i attempeted to started it, i had little to no compression. When i inspected it i found a fouled spark plug, and so i...


Take out your spark plug, but plug it into the plug-wire. Let the bottom of it dangle against the head and try to kick it. If no spark, problem with that, if it sparks, you may have a cracked head or piston/rings problems. This will at least rule one thing out.

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