More questions about my 125

I'm going to have my 2004 KTM 125SX rebuilt, and probably rejetted. As i can remember from before it blew up, it wouldn't make it up any hills (no matter what gear or what size of the hill), wouldnt give me anything in first gear around a corner, etc. If i were to rebuild it, and rejet it, would it run better? I CANNOT figure out why its doing this. Is there a different reason??

Sounds like you didn't have any piston rings left... new top end will make it rip like you wouldn't believe.

if it wouldnt go even in first then there are a few possibilities...worn out top end, jetting way off, ignition problem. Since it quit on you then the worn out top and/or jetting off ,causing a seize, would be likely.

sounds like you have to replace the rings/clean the power valve adjust/ rejet to a fatter main..change the needle to a 1469g 188/190 main is what i am running on my 06 125sx...it rips..also a 13--50 sprocket combo. does this sound right? also a 40 to 1 mix. the 06 settings should be fine i think...check in the jetting forum to be sure. i li ve in Utah..3500 to 5000ft mostly.

Can you give us any more details?

hard starting, compression, has anyone "worked" on it, did it just start running like this out of the blue?

has the stock jets, never changed, vertex piston, changed the rings everytime i took the cylinder off, has no compression right now, i think the cylinder is scratched, ran like crap after i replaced the first cylinder. I think my PV timing might be off. When i changed the cylinder, I never changed the piston (which was still decent,) could that be why? I remember i could make it up hills in every gear before i messed with it. It keeps going through cylinders and rings, and ( I always make sure I line up the piston ring correctly. I always mix the oil 32:1. The crankshaft as of last time i changed the cylinder did not move up and down. The bike only lasted one race without blowing up.

Until you pull the cylinder off and check it is all a guess. If you blowing up, which is a general term, then something is not being done right.

First, if this keeps happening you need to figure out the source. Either you have a burn down or break down. If the bike is burning down then the jetting needs to be sorted out or the crank seal is leaking. If the bike is breaking down, you may have worn crank bearings, improper X deminsion, power valve slide problem etc.

The connecting rod should have some play side to side but not up and down, perhaps you knew that.

For me to be much help I would have to know a lot more about the problem and that probably includes some pix. Clearly if you have no compression you are going to have to tear it down so there is no since in delaying it, GIT R DUN and let us know what it looks like.

is the piston in the right way?? Is the X dimension right?

I will check up on all of this, and keep you guys updated. Thanks!

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