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2003 125 sx not running

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Hey all, My son got a 2003 125 sx that hadn't been running in some time. Checked the top end and all seemed fine. Cleaned the carb out well, setting for float was good. Spark is good. Took the flywheel cover off and the timing marks were off by a bit so I realigned the marks. Still can't get it to run. Any ideas? the cdi looks like it has a crack in it...is there a way to test if this is good?

Thx 

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Hi, you can't check the cdi and KTM give no values anyway. These cdi's are discontinued so unless you can get a used one, you have to go post 2007 and require the plug and wiring as well, as the connector has changed. KTM now put the cdi under under the seat away from that silly position in front of the tank. The electrics tend to be trouble free and you say you have a good spark. It sounds like you have a fuel problem. Is fuel getting through? The plug (new plug?) should be wet if you are kicking it over and not starting. If it has been left standing the fuel emulsifies and absolutely gums everything up in the carb. I know you have checked  the carb, but did you remove the pilot jet and clean it - because of its design it can be hard to get the gum out of it. Maybe try another one. You need to remove the pilot, main and slide and blast every nook and cranny (Scottish words!) with brake cleaner using the plastic straw. Why was the timing out, presume you have set it back to the correct mark as there is one for the sx and one for the exc, although that wouldn't stop it starting. Also, if you have kicked it to death trying to start it, the cases fill with fuel and it will never start unless you bump it. Bob.

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Thanks for the reply Bob.

I put a new plug in and it is soaked after I kick it over so I believe fuel is getting in. I did take the pilot jet out and the main and let it sit in carb cleaner. I blew out everything with an air hose after. Maybe I'll put a new one in.

Not it sure why the timing was not aligned, I set it back so the marks line up.

ill try bump starting it to see if that will clean out the case.

thx again!

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You are obviously happy the carb is spotless .  Hopefully the cases are just full of fuel then. I would still try a new/clean pilot as well

Edited by 7Tktm

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HI, that's a good call although I presumed he would have done when the carb was off. Should check petals for chips and not closing correctly.

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no easy fix for my son! Looks like a crank bearing let go and it took out the cylinder and piston....haven't taken the bottom end out yet...good learning project!

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Wow, that's a real shame. Good enough reason for it not starting! Not the end of the world though, lots of us have been there. Sure you will get it rebuilt fine. Bob.

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Just rebuilt bottom and top end on sons '03 200sx, not a big deal. Waiting for parts was the worst thing. Take your time, follow the shop manual and have fun with it. 

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Waiting for my son to get his paycheque! Got the cylinder and split the case. Looks like it is the rod bearing on the crank that let go. Will take it in and see if they can rebuild it or get a new one. Will also order the piston and gaskets. 

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Hopefully you will manage an oem rod kit - they are the best. Presume you will be doing the mains and seals at the same time - with the cylinder and piston it will be like a new bike! Lets you then keep a proper maintenance schedule. Our 16 practice 125 nipped a ring at the exhaust port a few weeks ago, resulting in a scored bore. Used UK branch of Langcourt (you have one in the USA) and they did their usual excellent job. May well have been rust caused by condensation that did for your rod bearing, that's why I would get the mains done at the same time. These 125s are cracking good bikes that liked to be worked hard - make sure you use good quality fully synthetic 2 stroke oil. Good luck with it, will work out fine. Bob.

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Good info from Bronze except do NOT use synthetic oil to start with. Using dino oil for the first 6 or so tanks of gas will allow the ring(s) to seat properly. Synthetic is terrific oil but can retard the seating of new parts against each other.

Our 200 started on the 3rd kick and runs as good as new. The rebuild went really well and was time well spent with my son.

Other than that, follow the shop manual, ask questions here when curious, take your time, and your bike will turn out like new. 

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Update: Got the bike running and a big smile on his face! Rebuilt the crank, new bearings, seals, top end....Running great! Got all the parts and crank done thru Millennium Technologies just outside of Winnipeg, Manitoba, excellent service!

The hardest part was waiting for parts, no KTM dealers in Winnipeg so had to wait for deliveries

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