Modern Bike Question

[Mick Milakovic]

Hi All,
I've been chasing a ghost on my son's 2001 KTM 125SX.  It started running rough on the top end last fall.  I've cleaned the carb, pulled the coil and plug cap and looked for loose connections and cleaned grounds.  Air filter is new and clean.  The bike runs OK when cold but never cleans out on top.  As it warms up it runs even worse, sometimes momentarily cutting out but coming back when I chop the throttle.  When warm, half throttle seems OK, but not great.  It acts like my vintage bike did when the motoplat went out.  I haven't pulled the rotor and stator for lack of a proper puller, but that's where I'm leaning next.  Any thoughts or similar experiences?

Mick

[KJDonovan]

Mick,

One thing to double check, make sure there is zero paint where the coil is bolted to the frame.  While not a KTM, one of my neighbors had a WR250, same basic issues and the root problem was a bad ground on the coil. They shoot these frames with paint at the factories and never take the time to properly clear the paint where the coil attaches. I know you already pulled the coil, but do it once more and grind off any paint at the mounting bolts.

Thanks,

Kevin


Kevin J. Donovan
Foster, Rhode Island
72 Jack Piner (My Ride)
72 Six Day (Wifes Ride)
71 Suzuki TS125
72 Montesa Cota 123

[johnborn]

check the condition of the reed petals.

[wfopete]

Unlikely but if it's got some hours on it you may possibly have a dirty/stuck Power Valve.



Pete Petrick
175 Jackpiner
Slow but Good

[Gary Roach]

Hi Mick,

I'd have to agree with both John and Pete that it's probably a bad reed petal or stuck power valve.

Did you try changing the spark plug? I had a 250 once that started running bad on top end, and it ended up being a bad plug. I also saw another KTM that had the wrong plug in it that wouldn't run on top end either.

If the plug is not the problem, pull the reed cage and look at the reeds.

If you don't see a bad reed, next would be to pull the cylinder and clean the power valves. There are some good disassemble and cleaning procedures that can be found on the internet, like these two:

http://georgiaoffroad.com/forums/viewtopic.php?f=17&t=37449
http://georgiaoffroad.com/forums/viewtopic.php?f=47&t=21002

You're going to need a new top end gasket set, and while you have it apart, you might think about throwing a new set of rings on the piston.

Or, you can be really generous and give the bike away to me, and then you won't have a problem anymore!:D

Call me if you need any help.

Gary

PS:
It's good to see that your former student Zach Love is really tearing it up in the GNCC's!

[brian kirby]

This might be a long shot, but if it feels like its going rich on the top end, it could be the choke plunger. If that wears and wont seal properly, and the RPMs rise, it will draw fuel and go rich. This might explain why it gets worse as it warms up too.

Brian

[Don Roth]

Mick,
Another possibility is a plugged exhaust route,
will keep it from breathing ..
-don

[Mick Milakovic]

Wow, lots of options, but I can eliminate a few.  It's got a new plug, and I took apart the reed cage and the reeds were great.  

Kevin, when I took the coil off I made sure it was bare metal before putting it back on, and did the same for the electrical plugs.

Gary, I even took the cage assembly to the Love's house to look at, they have lots of experience with this model.  And yes, Zach is doing great on the GNCC circuit! He finished 8th overall and 1st amateur in Kentucky; we'll see what he does this weekend in Indiana.

Brian, you might be on to something because the choke lever was bent at one point last year and I straightened it, which would explain why it wore out, if it did.

I guess my next checks will be the exhaust route, choke plunger, and power valves.

Mick

[G Ellis]

Mick just bring it over to me I will help you. If you take the power valve apart you need a tool to set it back. I have that tool. You know you should just call me. Later Gary

[brian kirby]

Mick, I think Gary just gave you the correct answer to your problem.

Brian

[Mick Milakovic]

Gary and Brian, I laughed when I read it!  In all honestly, this is the best motorcycle group, ANYWHERE! [8D]

Mick