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2011 KTM 150 No Mid-Range - Power Valve?

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2011 KTM 150 low hours, nearly new piston, FMF fatty pipe, new bike to me. 

 

Runs great at low rpm and when on the pipe, but there's no increase in power from just off idle until just before it comes on the pipe. There's no surging or poor running anywhere in the rpm, just no power in the mid range, as though the power valve is stuck closed until it comes on the pipe.

 

I recently noticed that one of the power valve pivot 'axle' retaining plates was stripped (LH side of barrel) so the axle was starting to back out. I've ordered a replacement, but I don't think this could be the culprit.

 

Thoughts? Any input appreciated, I have zero experience with 2-stroke power valves.

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I dunno, but I had a 91 250 and it lost power..  At a race no less,  Tore it down when I got home and I find the power valve shaft had broke on the right side..  So I'd say you're on the right track there

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I dunno, but I had a 91 250 and it lost power..  At a race no less,  Tore it down when I got home and I find the power valve shaft had broke on the right side..  So I'd say you're on the right track there

 

I still have great power when it's truly on the pipe, so i think the valve opens, just not gradually as I believe it's supposed to.

 

Any other input?

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I still have great power when it's truly on the pipe, so i think the valve opens, just not gradually as I believe it's supposed to.

 

If the power valve is stuck in the down (open) position, you would have full power on the pipe, WFO.

The purpose of the PV is to give you more low and mid range.

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If the power valve is stuck in the down (open) position, you would have full power on the pipe, WFO.

The purpose of the PV is to give you more low and mid range.

It has good power just off of idle, far more than any 125 I've ridden, but as I said it just doesn't pick up until it's on the pipe. Could this still be a power valve that's stuck open? Seems like it's operating, but only at the two extremes.

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Removed power valve cover and confirmed movement when I rev it up. It looks like it moves a little later than other videos i've seen (higher rpm's than others). 

 

Adjustment was set different than i'd seen online. The mark on the moveable plate was just above the bottom mark on the non-moving plate. I've adjusted to the Langston setting.

 

Both control flap axles are 'stripped' in that the locking plates aren't retaining their position. I've ordered new plates and axles - is there a better locking plate available to stop this head stripping problem? 

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Have you removed both axles? The flap requires to be centred so it doesn't contact the cylinder as it moves to fully closed. The axles tend not to wear, but the o rings can leak after time, giving you a small smudge of gloop just below them. The retainer plates seem to wear quite quickly nowadays and should be treated as a service item before their 'teeth' wear away. They are just pennies and worth keeping a few spares. Bob.

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Hi Bob,

 

Axles have been removed to confirm they're still there, and i've re-installed with the flap set in the middle using shims on either side. I've doubled up on plates to cover more of the hex-head of the axles, hopefully that reduces wear.

 

Still doesn't feel like there's any real mid-range. Thoughts?

 

Dizo

Edited by dizo

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Do you have it jetted correctly for your conditions, particularly needle and clip position. You are obviously happy you have the pv system timed and opening/closing fully? The moving mark on the control arm should drop right out of view when fully open. We prefer the mark on the control arm to be just above the mark on the locking plate, but certainly worth playing about with the setting to see what you like. The 150s have a strong mid to top (or should have) so it's odd you are happy with the bottom and top but not the middle which makes me think maybe the needle.

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dizo,

Did you solve the problem? My boys 2012 150xc is doing exactly the same. PV set to Langston position. 

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