KTM 525 xc poor running
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  1. #1
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    KTM 525 xc poor running

    Hi guys i recently bought a 2008 KTM 525xc but i came with an issue. The issue is that the bike starts and runs fine but after riding it for a bit the bike stalls out and refuses to start. this is my first time owning a four stroke but i have worked on other two stroke bikes so i assumed it was the cooling system running poorly so i flushed the coolant and put in some new coolant in and checked that the fan was working i also opened the carb and cleaned out all the jets and the float. After i put it back together i sill did not run right so i pulled the plug and the top of the piston was very black as well as the posts on the pulg so now im not sure what to do. Does anyone have any advice? I can provide more detail if needed.

  2. #2
    Senior Member KTMATVHQ Guru
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    If you drained the coolant make sure you bleed the air out of the head. There's a small bolt and crush washer on the right side that you loosen to do this. Have you verified if the fuel tank is venting correctly? When it dies, pull the spark plug and make sure you still have spark. There have been a few XC's here that have had pickup coils go bad once they get hot. Another common thing is for the valves to get tight and cause issues. If they are tight on clearance they will loose clearance once hot, start holding valves open, and be hard to restart until the engine cools off. Verify they are within spec and adjust as needed. The intake boot between the head and carb on these is prone to cracking and sucking air. Sometimes you have to have this boot all the way off to see the cracking from the inside.
    Mine:
    2017 Husky FX 450
    2009 505 SX
    2008 525 XC-modded for mx (currently 450 cylinder)
    Dad's:
    2009 450 SX
    2008 540 XC

  3. #3
    Senior Member KTMATVHQ Member
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    Adjust your valves using 1/6th turn method only, check for ripped intake boot from carb to head.
    90% of the time it’s one of those

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  5. #4
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    would this cause the quad to backfire like crazy sometimes because mine does. I will try this but another issue that has arisen is that the throttle when pushed open fast does not accelerate and the engine dies

  6. #5
    Senior Member KTMATVHQ Member
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    Fix the no-run when warm first. Air leaks and misadjusted valves will make it run like crap.
    Yes, backfire is more than possible when in a lean or rich condition.

  7. #6
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    Make sure the hot start button isn't pulled out, I had that happen once and it didn't like to run. Is the backfire when you open the throttle or on decel? The exhaust has been known to not seal tight and cause pop on decel. Make sure your accelerator pump is working/adjusted correctly because that can cause an issue when cracking the throttle open. Was the carb taken apart by the previous owner?
    08 525xc ≡ 12.5:1 570 bbk, +1 valves, Crower Cam, Houser Bounce Nerfs, Razr 2 rears, Razr fronts, Pro Armor Dominator Bumper, Scotts Steering Damper, Mino Water Pump, FCI intake, KTMBill Skid Plate, FastRanchero 41mm Carb

  8. #7
    Senior Member KTMATVHQ Addict
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    Do/check all of the above. It also sounds like it’s running real rich. New plug and check what size your MJ is. You will need to go down some sizes on it.

  9. #8
    Junior Member Rookie
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    i do not know much of this bike in its previous life as i bought it from the owners father and he did not know what the son had done. but i belive the backfire happens as soon as you start to decel

  10. #9
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    What is an Mj?

  11. #10
    Senior Member KTMATVHQ Guru
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    MJ = Main jet in the carb.

    If it has the stock exhaust and it's a lighter popping on deceleration it's probably the head pipe sucking air where it mounts to the flange on the head. It was a common issue that can be fixed by grinding 1/8" off the front of the header pipe so it seals internally on the flange like it's supposed to.

    If it's a hard bang that is actually a backfire then it's probably too rich.
    Mine:
    2017 Husky FX 450
    2009 505 SX
    2008 525 XC-modded for mx (currently 450 cylinder)
    Dad's:
    2009 450 SX
    2008 540 XC


 

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