1996 ktm rxc 620 help!

Discussion in 'Thumpers' started by enduroracer3245, Mar 7, 2012.

  1. enduroracer3245

    enduroracer3245 Orange Crush

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    Hello fellow riders! So i got a serious problem on my hand with my beautiful 1995 KTM RXC 620 that i love to ride! So i will tell you from start to end on the information on what i got right now but i need some direction from some wise people being only i am 17 and my father doesn't really want anything to do with the ktm at the moment. I am very mechanical inclined so i can do most engine easy-moderate repair. Ok so now onto the description, my bike just idles but will not accelerate. Now before this happened i was doing some sandy hill climbs with friends on a cool summer day, my bike ran great and never shown any signs of this problem. Towards the end of the hill climb day i stopped to rest for a few minutes on a sand hill with my bike facing towards downhill, i go to start it and it make this sound like something fell into the engine but went away after a few quick seconds so i was like oh crap and just had my friend trailer it home for me. I get it started the next day and it runs fine but here is the scoop towards the end of the day for the road riding the bike would no longer accelerate like a 650cc would but like a little 110cc, like i had to give it full throttle to get off from stop lights. I made it home but by that time it really was running horribly to the point where if i gave it gas it would just shut off. So far the thing i have done to the bike is replace the plugs, cleaned the carburetor, and petcock but no absolute change at all. Also 2 weeks before the hill climbs we had to pull the magneto cover off to replace some oil lines but i moved the magneto back to is original spot and made sure it was in it's original spot, I made a note that it didn't drive any different and was normal as i was riding around town for those 2 weeks after the oil lines and magneto cover were taken off. Only after the hill climbs it started running like crap. I don't even know where to start on fixing it but i am so close to just taking it to the ktm dealership about 120 miles away to have them look at it and fix the problem but i am trying to save money. Thanks to any wise people that answer this to help, i am just lost at the moment and i need to get my hands back on this project so i can ride as spring is approaching and our gas prices are going up :). Good gas mileage for a enduro bike though!

    Thanks Adventure Riders!
    #1
  2. enduroracer3245

    enduroracer3245 Orange Crush

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    Anyone? I am so stumped on this problem.
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  3. mcma111

    mcma111 Long timer

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    First off I'd pull the air filter and have a look inside the intake to make sure that sand didn't get in there. If it did it's time for a top end over-haul. You may have damaged the piston either way. Take a compression test to confirm compression.

    This is just for starters.

    Good Luck.
    #3
  4. enduroracer3245

    enduroracer3245 Orange Crush

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    Alright thanks, I will do a compression test.
    #4
  5. mcma111

    mcma111 Long timer

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    When you do the compression test do it a second time but squirt a small amount of oil in the cylinder and spin the motor over a few times before testing again. If the pressure rises then it's the piston and or rings.
    #5
  6. rz35027

    rz35027 Been here awhile

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    Throttle cable still connected?
    Gas tank vent?
    Check the valves...
    #6
  7. IheartmyNx

    IheartmyNx Ihave2draft

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    plug fowled?


    I'm thinking when you parked it on the hill oil got by the thing-ma-jig and crept into the carb, fowling the plug.


    And x2 on checking the valves. I'd pull the cover and check the cams and the whole thing. Oil might have loaded up and when you started pumping more, blew something.
    #7
  8. bmwktmbill

    bmwktmbill Traveler

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    What carb?
    If it's a CV carb the diaphram is torn.
    Or maybe the carb is loose?
    bill
    #8
  9. enduroracer3245

    enduroracer3245 Orange Crush

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    The carb is a Kehin FCR MX 39mm. I think there is just one diaphragm on it but i will check to see if there is more. Thanks for adding to things i can look at to get it running again, it helps alot!
    #9
  10. enduroracer3245

    enduroracer3245 Orange Crush

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    Thanks everyone for the answers!
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  11. enduroracer3245

    enduroracer3245 Orange Crush

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    I am buying diaphragms soon i will let you guys know if it works or not.
    #11
  12. mcma111

    mcma111 Long timer

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    What diaphragms
    #12
  13. enduroracer3245

    enduroracer3245 Orange Crush

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    Well there are 2 diaphragms in the Keihin FCR MX 39mm carb. If there is a tear or even just a little puncture on them they make the bike idle fine with no notice but if acceleration is thrown at the carbs they cannot handle it because the diaphragms leak. The one diaphragm is on an accelerator pump for fuel and the second one is for air and if one or both are not working in sync with the carb it will run like crap from what i have seen on the internet and once bmwktmbill had said to check them it got me thinking about it because we just had pulled it off before that hill climb to clean and inspect it and might have left a pin sized hole which went unoticed until the rip got bigger from doing all that acceleration causing a big difference. See after awhile i have heard that these diaphragms get stretched out and when you take the carb apart and put it back together the diaphragm will be bigger than its mounting spot, so when you put the cover back over it it cannot stretch anymore cause it has its full life causing it to rip. I will post pics to tomorrow of the diaphragms if there is any tears or rips. Its hard to explain in text form but pictures will be easier.
    #13
  14. mcma111

    mcma111 Long timer

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    KISS

    Have you even done the compression test yet or are you just going to start throwing parts at the bike in the hope that something you do some how fixes it???
    #14
  15. enduroracer3245

    enduroracer3245 Orange Crush

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    no i haven't bought parts yet, i get my bike in the shop tomorrow and then i am doing the compression test first and then taking the carb back apart to look at the diaphragms for any rips or tiny holes.
    #15
  16. enduroracer3245

    enduroracer3245 Orange Crush

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    Alright i got a picture of the plug and i know its running rich since i first got it but its because of the jetting but do you guys see any signs of pre-ignition? Oh also i did a compression check and everything checks out to be fine!

    [​IMG][/IMG]
    #16
  17. rz35027

    rz35027 Been here awhile

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    Yikes... if the colours in the pic are right, that looks lean to me
    #17
  18. enduroracer3245

    enduroracer3245 Orange Crush

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    That would be the flash my RAZR's camera flash is a little to bright sometimes. but its black from what I am seeing. :)
    #18
  19. Sundowner

    Sundowner Bort

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    Does it run better with a clean plug in it? Have you checked the valve rocker gear yet, in case you've broken one arm? Take the radiator cap off when the engine's cold, start the motor - can you see lots of bubbles coming up through the coolant as the engine warms up to hot? Looks like something stuck to the old plug electrode but it could just be carbon from the flogging it's received during the hill climbing. Any sign of white smoke from the exhaust?
    #19
  20. enduroracer3245

    enduroracer3245 Orange Crush

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    alright update on the status! We put a new plug in, fresh gas, fresh carburetor rebuild, and carburetor tuning but it did not change anything at besides that the E3 spark plug just does not die and cleans itself from fouling up. We did a compression check and it came in at a whopping 130 PSI so i do not think compression is an issue. Kind of funny that I can stand on the kick lever and i am about 260 lbs at 6'6" and it slowly went down so its doing find on compression. we found 2 factors that were looking at though, we have the choke cable that screws into the carburetor and found that to be very loose and not sealing correctly possibly causing a too lean or too rich condition. The decomp lever seems to be finally singing its last note as the clanking noise is most likely coming from that, I have heard this on other forums of the decomp making this loud spine tingling noise that makes the bike sound like its falling apart. We are going to fix those 2 problems and see where that leads us and let you guys know.
    #20