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Ktm 125 feels gutless on bottom end

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I have a ktm 125 believed to be the tyla rattray 2005 edition I've recently put a new vertex piston in. I was having problems with it bogging and misfiring but that seems to be solved since I swapped the br9 iridium plug for a standard br9 plug. The bike doesn't seem to have any low end power at all I'm just wondering if this is normal for ktms as my friends yz 125 seems to pull a lot better on the bottom end before the powerband, my ktm has a 13 tooth front sprocket and 49 on the back would putting a bigger rear sprocket on solve this issue ? Thanks

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Hi, they came standard with a 13/50. You could try adjusting the power valve to open earlier. Is it still misfiring - you should check for air leaks between the filter and engine side of reeds + reeds themselves.  Bogging is normally down to incorrect jetting.

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9 times out of 10 the PV isn't connected properly.  It is very easy to mis-align the the linkage when you're installing the cylinder, been there, done that.  Take the PV window off the side of the cylinder and see if they are lined up...it is the one behind the pipe.

 

If the bike stutters, and has trouble getting going, but revs cleanly on the stand, then likely it's a PV issue.

 

I've been around here for a while now, there are very few members who have the knowledge that 7ktm has.  He knows his stuff, so I'd listen to his advice, and I am not trying to contradict him...

 

The PV is the easiest place to start, if that checks out then dig in to carberation, etc.

Edited by poldies4
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Hi, they came standard with a 13/50. You could try adjusting the power valve to open earlier. Is it still misfiring - you should check for air leaks between the filter and engine side of reeds + reeds themselves.  Bogging is normally down to incorrect jetting.

It doesn't bog or misfire anymore since I changed to a standard br9 plug, I don't know what the issue was with the iridium plug but the bike hated it, I'm going to have a look at the powervalve give it a clean ect and check timing thanks for the info.

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9 times out of 10 the PV isn't connected properly.  It is very easy to mis-align the the linkage when you're installing the cylinder, been there, done that.  Take the PV window off the side of the cylinder and see if they are lined up...it is the one behind the pipe.
 
If the bike stutters, and has trouble getting going, but revs cleanly on the stand, then likely it's a PV issue.
 
I've been around here for a while now, there are very few members who have the knowledge that 7ktm has.  He knows his stuff, so I'd listen to his advice, and I am not trying to contradict him...
 
The PV is the easiest place to start, if that checks out then dig in to carberation, etc.

Is the power valve window the 1 on the left side of the cylinder ? What do I need to look for exactly when checking it's connected properly I've never done this before thanks

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14 minutes ago, Dale125 said:


Is the power valve window the 1 on the left side of the cylinder ? What do I need to look for exactly when checking it's connected properly I've never done this before thanks

There are 2, one right (brake side) one left (shifter side).  The window that shows the linkage is on the right, just behind the expansion chamber.  The one on the left will show you your current setting.  7ktm could likely explain the adjustment better than I can.

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Hi, if your bike has plenty of top end then the pv should be connected ok. Have a look in the left hand cylinder inspection cover (one with 2 x 6mm bolts) - you will see a metal plate with a slot in  it (call it the control slot) nearer the exhaust flange and another piece with a slot beside it but on the cylinder side. This second piece will move down as you rev the engine and go back up as you close the throttle. If you want bottom end you need to adjust it so that the inner slot is higher than the 'control' slot. When we had our pre 16 bikes my son preferred the slot to be almost out of sight at the top of the window. Other riders prefer it lower down (Langston setting?) to increase mid/top. Really depends how you ride the bike to get what is your optimal setting. Hope this helps. Bob.

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If the pv checks out ok richen up the carb on the bottom. 

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The 125/200 has a very unique set up. It's in the front behind the pipe. I didnt see any way to access it in the bike  on my 04.  

 

 Pull the left side cover to check setting and if working.

It's pretty easy to not engage the pawl/ foot when installing the cylinder. 

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