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HOT 2003 KX125

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I bought an 03 KX125 that needed a top end, 3 months ago. i have decided what I will be doing with it. I'm buying a Namura top end kit (I'd buy Weisco but I dont have $200 for a top end kit), having it ported and keeping it. When I took the top end off, I was surprised with what I saw. The plug was really dark (not fouled), the piston had a carbon deposit (black spot) on the underneath of the piston, and on the left side of the crank (inner piece right beside the rod) was a dark blue. I know these are due to over heating. What i would like to know is would it be caused from wrong fuel mixture, improper jetting or the air/fuel screw leaned way too far out? I plan on checking the jetting before I install the top end and if its not stock, re-jetting it to stock spec. If it is at stock spec, what do you guys think it would have been? I would like to sort it out before I break in the bike. Thanks  :)

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I know that could be caused by a lean fuel mix or jetting issues. But im fairly sure (i might be wrong) that you have a right and left side crank seal. The left one is dry and the right one is wet (oil). Now if the left side one is torn, broken down, blown out, etc. it can also lean out the mixture alot. U might want to check it out. Its behind the rotor on the left side case

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I know that could be caused by a lean fuel mix or jetting issues. But im fairly sure (i might be wrong) that you have a right and left side crank seal. The left one is dry and the right one is wet (oil). Now if the left side one is torn, broken down, blown out, etc. it can also lean out the mixture alot. U might want to check it out. Its behind the rotor on the left side case

Thank you very much! I would have never thought of that. I will definitley check that next time I'm at my uncles (with his help of course). Updates will be posted as soon as I get the info  :)

 

Edit: I texted the guy i bought it off of this morning, and asked what he mixed it at and what happened when it went.

 He said that his son told him "It sounded and acted like I hit the kill switch. it just died out" 

 

I mainly want to know what caused the small nick on the port (maybe 1-1.5mm wide, 1.5 mm long and .7 or .8 mm deep on a downward angle on the bottom of the port) & groove on the piston. Wrist pin bearing pin/rod?

Edited by ReturnOfJorddo

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The crank bluing is most likely from assembly. The crank web is heated with a torch to expand it and make slipping the big end pin in much easier. Many bikes come from the factory with blue heat marks, and many shops will do the same trick.  To get hot enough to blue that area while running the big end bearing would have to get EXTREMELY hot, and would clearly be toast, either locked up, or in a zillion pieces.

 

Underside of the piston being carboned is from running hot. Could be jetting, could be poor grade fuel and detonation, could be improper engine setup (squish, compression, etc) and detonation, could be overly advanced ignition timing, etc etc etc.

 

The nick sounds like it's from a bearing roller or  possibly a piece of ring. Time to do some investigation on what's missing from where.

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Pictures would help. I would inspect the crank really well. Nicks in the cylinder are usually steel related.

 

You should look at the PRO-X pistons instead of the Namura. You can buy a complete top end kit inlcluding gaskets and wrist pin bearing for under $100 on ebay. I know I just bought one for my 01 250 for $109 shipped. 

 

Sorry yours is $102.95 shipped...lol

http://www.ebay.com/itm/ProX-Pro-X-Top-End-Piston-Kit-Kawasaki-KX-125-KX-2003-/261261622654?pt=Motorcycles_Parts_Accessories&hash=item3cd467fd7e

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The crank bluing is most likely from assembly. The crank web is heated with a torch to expand it and make slipping the big end pin in much easier. Many bikes come from the factory with blue heat marks, and many shops will do the same trick. To get hot enough to blue that area while running the big end bearing would have to get EXTREMELY hot, and would clearly be toast, either locked up, or in a zillion pieces.

Underside of the piston being carboned is from running hot. Could be jetting, could be poor grade fuel and detonation, could be improper engine setup (squish, compression, etc) and detonation, could be overly advanced ignition timing, etc etc etc.

The nick sounds like it's from a bearing roller or possibly a piece of ring. Time to do some investigation on what's missing from where.

I will post pics when I get home as I'm on my phone on the bus lol.

Pictures would help. I would inspect the crank really well. Nicks in the cylinder are usually steel related.

You should look at the PRO-X pistons instead of the Namura. You can buy a complete top end kit inlcluding gaskets and wrist pin bearing for under $100 on ebay. I know I just bought one for my 01 250 for $109 shipped.

Sorry yours is $102.95 shipped...lol

http://www.ebay.com/itm/ProX-Pro-X-Top-End-Piston-Kit-Kawasaki-KX-125-KX-2003-/261261622654?pt=Motorcycles_Parts_Accessories&hash=item3cd467fd7e

I live in Canada, so not only do I have to pay shipping, I have to pay import charges. Sucks balls lol.

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I ordered a wiseco top end for my kx250 for about 160 shipped from gnarlyparts.ca

Here one for you

http://gnarlyparts.ca/product_info.php?cPath=5978_2427_8742&products_id=44518

THANK YOU SO MUCH, YOU ARE THE MOST AMAZING PERSON EVER. I can get a full top & bottom end rebuild off there for $350, I'm gonna see if my dad will go 50/50 on it for me. Thank you soo much!  :thumbsup:  :worthy:

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Wasn't too lean where it was mostly being ran, but still could be far too lean.

Example - my yz had a 58 pilot and 152 main when I got it. Was a burbling, plig fouling mess, but would detonate and bog at wot. So the plug camw out dripping wet and black, but it would have killed itself lean if I road it more than that 1st shake down run.

I ended up around a 45 pilot and 172 main.

Just saying, don't not-check jetting because of a black plug.

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Wasn't too lean where it was mostly being ran, but still could be far too lean.

Example - my yz had a 58 pilot and 152 main when I got it. Was a burbling, plig fouling mess, but would detonate and bog at wot. So the plug camw out dripping wet and black, but it would have killed itself lean if I road it more than that 1st shake down run.

I ended up around a 45 pilot and 172 main.

Just saying, don't not-check jetting because of a black plug.

I plan on checking the jetting as soon as I can. If it's not stock I'll re-jet it to stock specs. I plan on running 32:1

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