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Washington MOUNTAIN RIDING

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HAS ANYONE WITH A KTM 4 STK. EXPERIANCED LOSS OF LOW END OR RUNABILITY ISSUES WITH THE O-RING MOD ON THEIR ACCELL.PUMP WHILE RIDING AT 3K TO 6K ? I ALREADY CHECKED THE TECH FORUM AND FOUND VERY LITTLE ON THIS. IT SUCH A LONG DRIVE TO MAKE JUST FOR TESTING SO I AM HOPING FOR FIRST HAND EXPERIANCE.ITS A 2009 450 XCF W/FMF QUIET CORE AND A JD KIT SET TO 3-6K AT THIS TIME.IT ACTED THE SAME AT 0-3K SETTINGS ASWELL. 

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I don't have a KTM but I do have a CRF250X with JD jetting that has rough throttle response off idle while riding, and I'm sure any increase in altitude or temp will make it worst, so I'm trying to fix the problem before I start riding the mountains.  With my XRs sealevel jetting works to above 5k with some blubbering on a hot day, I usually turn in the mixture screw and live with it for a one day ride. 

A clue to your issue would be when did the problem begin.

 

I'm currently running my FCR without the O ring so there is less squirt off idle, but that is because of the above mentioned problem. There is also a clearance adjustment on the AP linkage that can delay the squirt off idle. I don't have any squirt just off idle, the richness is at about 1/16 to 1/8 throttle. My off idle richness creates a ragged throttle response when opening the throttle while riding, the stumble and abrupt power making riding difficult. I've had similar problems with XRs that were easy to fix with minor jet changes but the FCR on my X hasn't been that easy.  Incrementally I have  lowered the JD red needle one clip, one size smaller main, and a slightly lower float level; the last seemed to make the most improvement.  One more test ride and maybe I can  start incrementing back to JD recommendations.

 

The XR service manuals have a good section on jetting for altitude and temperature. For the PNW mountains  I start with the mixture screw and sometimes the needle.

 

Jetting for Altitude & Temp.JPG

 

Jetting for Altitude & Temp Instr.JPG

Edited by Chuck.

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I have a 530 fwiw, you need to shorten the pump travel (thicker rivet or spacer) or go to a bigger leak jet. Both sorta do the same thing. Taking the o ring off isn't enough because the spring is plenty strong (I don't use it)   just got back from 6-10k, 3-6k should not be a problem for ya, Was it a real hot day" did you try tuning the fuel screw?

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I have a 530 fwiw, you need to shorten the pump travel (thicker rivet or spacer) or go to a bigger leak jet. Both sorta do the same thing. Taking the o ring off isn't enough because the spring is plenty strong (I don't use it)   just got back from 6-10k, 3-6k should not be a problem for ya, Was it a real hot day" did you try tuning the fuel screw?

pump travel is shorten with that spacer pressed on the bottom of the diaphram,the temp was mid 50's to mid 70's. the gap at the timing screw is .310" fuel screw started at 1.5 turns.went to 1.75 because we were at maybe 4k and it was cool.felt little to no change . when you say you don't use it you are referring to the o-ring not the spring rite?

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I don't have a KTM but I do have a CRF250X with JD jetting that has rough throttle response off idle while riding, and I'm sure any increase in altitude or temp will make it worst, so I'm trying to fix the problem before I start riding the mountains.  With my XRs sealevel jetting works to above 5k with some blubbering on a hot day, I usually turn in the mixture screw and live with it for a one day ride. 

A clue to your issue would be when did the problem begin.

 

I'm currently running my FCR without the O ring so there is less squirt off idle, but that is because of the above mentioned problem. There is also a clearance adjustment on the AP linkage that can delay the squirt off idle. I don't have any squirt just off idle, the richness is at about 1/16 to 1/8 throttle. My off idle richness creates a ragged throttle response when opening the throttle while riding, the stumble and abrupt power making riding difficult. I've had similar problems with XRs that were easy to fix with minor jet changes but the FCR on my X hasn't been that easy.  Incrementally I have  lowered the JD red needle one clip, one size smaller main, and a slightly lower float level; the last seemed to make the most improvement.  One more test ride and maybe I can  start incrementing back to JD recommendations.

 

The XR service manuals have a good section on jetting for altitude and temperature. For the PNW mountains  I start with the mixture screw and sometimes the needle.  thanks for the input.the problem appears to be intermittent,usualy after a short blast of 3/4 or wot and then backing off to 1/4 to 1/2 it will shoot ducks. only way to stop it is to ride easy for a short spell or downshift and clear it out like a 2 st. and it has to be 3k feet or above   .my xr barely needs a idle adj.when I leave sea level and go to the mtns.   :thumbsup:

 

attachicon.gifJetting for Altitude & Temp.JPG

 

attachicon.gifJetting for Altitude & Temp Instr.JPG

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okay finaly got it figured out.my 09 450xcf has no leak jet.jd jetting sent me a modified float bowl that has provisions for a leak jet.so jd kit 3kto6k settings and a #60 leak jet,o-ring mod on acc. pump timing screw. timing screw set at 2.75mm. 92 unl. pump gas .throttle response is extremely crisp and instant. fuel mileage increased. I guess most people are getting to know f.I. I am still playing with carbs. oh by the way that was at only 3k to 6k temp. mid 70's on sat. today at sealevel the kid said it was bad fast.  thank you J.D.

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My '04 450 EXC got the same help from JD with a different float bowl and thus leak jet.  That added low end and kept me from having to run summer mountain jetting and then winter wet side jetting every year.  Now it's good enough that I just ride with it and enjoy not having to spend my time swapping needles.  I ride Giff/Entiat/Foggy Dew, all of which get into the 6k range at least.  We're so lucky that JD is native here ... he really is a national treasure!

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