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Discussion Starter #1
Hi all, I recently bought a KTM 200 and discovered a problem with it. The bike had been running perfectly at the bottom end but felt really choked at the top. I figured it was just running rich in the cold weather or possibly a gunked up power valve. I decided to take the bike apart over the xmas/new year period and have a look at the top end.

When I took the power valve mech apart I found it was actually quite badly damaged. See pics (control shafts should not be in 2 bits!).

I can only think that the control shafts seized and ground the teeth of the horse shoe piece and broke the shafts in two. The mechanism seemed to have been put together properly, I didn't noticed anything out of place when I was taking it apart. Maybe someone was asking too much of it?

I have absolutely no experience with power valves so if anyone has any experience of this or any clues on how it may have happened it would be appreciated, I don't want to replace the bits and put it back together and end up with the same problem!

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If the control shafts were seized in with coke build up, how did you get them out, mine were hard enough to remove the first time I removed them, and they were complete. The power valve is controlled by a centrifugal mechanism behind the clutch case, basically the higher the RPM, the more the am moves. I'm surprised it had enough power to break anything.
They are known to get jammed up if they're not cleaned, so maybe that's what happened. Does'nt look too expensive to repair.
 

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Just a thought. The power valve got jammed up with coke through lack of maintainance and the bike started to run rough. Then somebody trying to work out was wrong used a screwdriver to try and lever the mechanism free, breaking teeth on one part and shearing the control shafts. It sounds far fetched, but I can't imagine how else that would have happened. Realising they had fucked it up, then decided to sell it. You said you'd just got the bike? I can't imagine the old owner didn't know anything about it.
 

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Discussion Starter #5
This is the thing, the control shaft on the left pretty much dropped out with a bit of shaking. The right side was a pain and I had to push from the port side. It was fairly stiff but tbh if it hadn't been broken in two I don't think it would have been too much of a problem to get out.

There wasn't much coke build up at all there, loads on and around the main valve and throughout the exhaust (a result of it running rich with the valve out of action presumably). I'm starting to think the cause may have been the control shafts catching on the back side of the port, it looks a little rough round the edges, so difficult to see and too small to poke a finger down there!


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Discussion Starter #6
The horse shoe piece is warped, it looks like a lot of force has gone through it. I don't think someone had been at it recently, it all seemed like it hadn't been opened for a long time or if ever. But sure I think they must have known there was a problem, I just think they were too lazy to figure out what it was.
 

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The barrel is only ally, so there should be some witness marks. Anyway, I doubt that it's from snagging the edge of the port, there's a fair bit of clearance when it's all clean. I don't thing the centrifugal mechanism is powerful enough to shear the shafts and break teeth, plus warp the control plate (wotever it's called) It would bend the connecting arm first, surely.
 

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The control shafts also look quite clean for something that hasn't been apart in ages?? I think the burring on the end of the control shaft was done by someone trying to remove it. Are there any hammer marks on the ends on the shafts? I'm more inclined to think that was done by someone trying to fix it, rather than the bike fucking itself up. I'm only guessing though, so don't go out and kill the guy you got the bike off. :D

I remember the first time I took the powervalve out on my 200, it was black. and I mean really black, everything...not like yours which looks like it's been cleaned quite recently..
 

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Discussion Starter #10
I guess that damage to the end is likely to have come after it broke as they would probably be rattling around in there with the engine running.

So I've only taken apart the top end, would it be wise to have a look at the other end of the connecting arm? I'm curious to find out how it works down there and might give me some peace of mind. How easy is it to get to? I don't want to spend all my time off work working on this bike!

The top of the connecting arm seems to look ok, it's very slightly flat spotted on one side but I'm it wouldn't cause a problem. I can feel its sprung to one side and moves fine.

View image: photo (2)
 

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Discussion Starter #11
I have cleaned a fair amount of it already, unfortunately I didn't take pics as I was taking it apart. All along the main port/control flap was coked up pretty badly and I had cleaned most of that off before taking the photos. But the extra ports on the sides that the control shafts open have only been doused in WD40 and wiped as I was trying to get out the broken ends.

I do feel like someone has put it together badly and the control shafts had broken immediately after and its been run like that since. I can't be bothered to blame, I would prefer to have my bike running sweet!
 

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You have to drain the oil and coolant, then remove the clutch side casing to get at the power valve centrifugal mech. I've never taken one apart, so can't comment too much on the difficulty of taking it apart. The flat spot might not be good though, I think I remember reading something about that. It wears over time and needs replacing, so taking it apart to check and replace the arm might not be a bad idea.
 

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Discussion Starter #13
Ok, the arm is only £7.50 so I'll replace it. Thanks for your help nick :) hopefully my next update will be in the new year with the bike running like a dream!
 
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