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Ktm 300 xc Wont build rpm's or power.

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My wife's 2014 KTM 300 suddenly lost all power past 1/3 throttle. Won't build rpm's at all. Any thoughts on what to look for.. I am kind of at a loss. Here is what I know. Bike was running great. Then suddenly lost power and had to idle back at 1/4 to third throttle. Wide open and it burbbles out. Idles fone and seems to build rpm in neutral but mayne still not quite right. She rides pretty mild and doesn't flog it too hard by any means. Bike is still stock top end. Not sure exact hours but i would guess under 100 for sure. Oil is changed religiously.. though i'm going to check it for metal and signs of bottom end issues next as I have not yet check this. Jetting is and was good. Plug had minor fouling and was indicative of a rich burn if anything and not grossly rich. We were riding sand so I cleaned carb, and air filter thoroughly. Pilot jet did seem to have some sand or debris so i removed that and put it back together. Thought the sand in the pilot might have caused the issue so finished cleaning it and reassembled. Put a new plug in it and took it our for a ride, no go.. still not running right.. what gives? Is this indicative of a crank bearing? Is the power valve sticking? Do I still have sand hidden in the carb somewhere not obvious to me. Main jet and needle jet are clear... I noticed that the power vakve adjustment screw was like all the way in.. seemed not right but I hadnt messed with it in forever.. so i loosened it up all the way, like two turns from all the way out... no difference at all. Thanks for the help guys. I run two strokes because they are simple and I can usually figure this stuff out myself, but I am at a loss..

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Hi, first you need to unscrew the power valve screw flush to the case. if problem still there, check your main jet because is probably broken. If not, check the reedvalve block if not broken. good luck !

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You say sand. Did you suck sand through the motor. Not sure on hours?....have you checked the top end. It's probably due if you think it's close to 100hrs. If I saw sand in the carb, I'd be tearing into the motor.

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Yes riding in sand. I Did pull exhaust to inspect motor. No evidence at all of damage. Not a single blemish on cylinder walls. No real sand in carb. Just the slightest fleck that "might" have been aggecting the pilot jet. Didnt even wiggle the powervalve though, so i will pull exhaust again. Main jet is fine. Powervalve and reeds are next in my list to check

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PV linkage got loose?

silencer packing full?

reeds all beat up?

clogged main jet?

lets start with these.

Edited by billtro11

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Check carb vent lines for any restriction.

Exhaust restriction?

Sediment/rust in the carb bowl happens. It comes from the gas tank and not the air filter and usually doesn't make it to the cylinder. It might plug a jet, but you've eliminated that. It might plug a carb passage, but that would have different symptoms.

 

 

 

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Likely my exhaust silencer/spark arrestor. Its an fmf turbinecore 2. The mid-plate just befire tuebine is totally cracked and has allowed center tube to dislodge which lossened packing and probably clogged exhaust. New exhaust on order but my money is on that... Full disclosure... My wife discovered it because she said I wasn't showing enough enthusiasm for fixing her bike! Bahahaha! Wifey always wins.

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I have the same issue that has suddenly happened to my Ktm 300 xc. The last ride it was fine. The Next time I cranked it up it suddenly would not build rpms. It acts like it's loading up as if rich or fouling a  plug. I thought maybe the Jets got plugged up, so I cleaned the carb. The pilot did have some pluggage but that didn't fix it. The top end still has good compression. It has good fire but I put in a new plug anyway and that didn't help. I was wondering if a new spark arrestor did fix the problem on this original thread? 

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Recently had something similar happen to me. It turned out to be the power valve sub port had seized and wouldn't let the power valve to fully open.

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On 7/11/2017 at 10:32 AM, bradcutter said:

Likely my exhaust silencer/spark arrestor. Its an fmf turbinecore 2. The mid-plate just befire tuebine is totally cracked and has allowed center tube to dislodge which lossened packing and probably clogged exhaust. New exhaust on order but my money is on that... Full disclosure... My wife discovered it because she said I wasn't showing enough enthusiasm for fixing her bike! Bahahaha! Wifey always wins.

This is the key to a "happy" marriage. Always remember the Wifey always wins (or at least make her think so!)...

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18 hours ago, motox745 said:

Recently had something similar happen to me. It turned out to be the power valve sub port had seized and wouldn't let the power valve to fully open.

Remove PV valve rod cover and actuate linkage by hand to see if its jammed up. 

 

Honestly sounds like a choke or reed problem.

Edited by theBIGnaud

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This sounds a lot like what my 2015 250->300 xc did.  The first 1/3rd throttle would be fine, but sort of hang and sputter between 1/3 to 2/3, like the powervalve was sticking and most noticeable in the first few gears with a rolling throttle.  After a lot of messing around with jetting, the fix ended up being the installation of a JD Jet Kit and adjusting as the instructions described. 

Prior to this, I tried a n2zh (or something like that) and infamous NECJ suzuki needle and both exhibited the problem unless it was cold (like 5-7 Celsius) and once it got any warmer, the stuttering symptom at 1/3 ish throttle would show up again with a vengence. An elevation increase would do the same. With the warmer weather, I'm noticing a very slight bit of stuttering again, but can fix that by changing the clip+needle as per the kit instructions.  

If I could do it over again, I'd go straight for the JD kit instead of wasting all that time, money, fuel, and frustration trying to dial it in with the infinite permutations of needles, clip positions, main jets and idle jets vs elevation/temp.  

Another issue I had was I had the main jet rattle out completely on a ride, so past 1/4 throttle, the bike would just gasp and choke.  Pretty surprised it even ran.  

 

 

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