KTM 125 SX issue

[Corban_White]

So, I did some testing with the compression tester, and it is junk, but the gauge is fine. The hose it the problem. Too much flex in it so it's not transferring the pulses to the gauge. When I tested my ATK and the kids 4wheeler I could feel the hose flexing. When I tested it with the solid pipe it gave much better numbers. I'll probably be looking at a different tester.

Looking at the jug, there is only the one scratch that catches my fingernail, but I guess that's enough. I wish Millennium wouldn't have changed their pricing structure to an all inclusive repair because sometimes you just need a replate... Oh well, it is what it is. Like I said, I don't mind doing what needs to be done, I'm just not in the camp of replacing all possible wear items when something is apart. In run to failure mode, you do have to replace/repair failed items, I just want to be sure they are failed before I do! 😉

As a side note, I'm planning to put in the piston from the 07-15 motor because it has 2 rings.

 

[rholbrook]

I have used these guys eveytime and have been completely happy with their work

 

[Corban_White]

Awesome, thanks Russ!

 

[Corban_White]

So, to update this thread, I sent the cylinder to Millennium (because they had a week lead time plus a week shipping each way and Power Seal was a 4 week lead time plus a week shipping each way), got it back and installed with a new piston....and it ran exactly the same. So I replaced the CDI with one from a 2007 (2006 is discontinued and not available) and it ran great, but blubbered as soon as it got on the pipe. After some testing I figured out it was jetting (PO must have had to richen it out to compensate for the low compression??) and after going from a 185 to a 180 main and dropping the needle one clip it runs amazing. This is the only 125 I've ridden, so I thought how it ran before was just how they were (it ran good, but wasn't exactly a powerhouse). NOT SO! On hard pack this thing pulls almost like my 300 did! I'm sure I would notice the difference in sand, and it doesn't have quite the low end torque of the 300, but it isn't far off for my kind of terrain. My son is loving it!







TLDR; the problem was the CDI, but the other things I fixed also needed doing and made the bike a ton more fun.

 

[Rot Box]

Good to hear all is well. Good to see the ATK getting used too 😎

 

[Gravy]

Glad to hear you got it sorted!
125s are way fun!
They are a bit trickier to jet because they don't have as much vacuum signal as a bigger cylinder.
And with lower compression you are correct that it would take a bigger jet to pull the same amount of fuel.

 

[rholbrook]

I see a bright future for your son and you.