950 carb refurbishing - pitfalls and experiences, please?

Discussion in 'Dakar champion (950/990)' started by Orange Toaster, Feb 28, 2013.

  1. slackmeyer

    slackmeyer Don't mean sheeit. .

    Joined:
    Jul 23, 2007
    Oddometer:
    4,385
    Location:
    Berzerkeley, CA
    I'm bumping this thread, because my 950 has been having more and more carb problems- it's always popped on decel, and I've only been able to tune that out by making it way over rich, which I am not inclined to do. Recently it's been doing more and more popping and backfiring through the carb at very small throttle openings and when I close the throttle at 2-3k rpm. Makes it very hard to ride around town. It also occasionally dies at stop signs. Bike runs amazingly well under hard acceleration over 4k rpm.

    This bike has 65k miles on it.

    I've taken the carbs apart as much as I can short of splitting them (didn't see any reason). soaked them in pine sol and cleaned them really well. I've checked and rechecked float height (3.5mm), pilot jets (cleaned many times, and it acts the same with 42 or 45 jets), needle positions, air jets (all stock), linkage play (there is some, but it seems like the butterfly return springs should take that up). Sync'ed the carbs, checked the TPS. Been all up and down different jettings, it doesn't seem to make any difference.

    Oh, I've also swapped carbs with a friend (made it run much much better), and then matched his settings (did not help on my carbs).

    So, I'm open to any ideas. I'm starting to think it's either worn out/stiff diaphragms/slides (I may swap these with my friend to test), or air leakage into the carbs through various places.
    #21
  2. Balsta

    Balsta Been here awhile

    Joined:
    Feb 11, 2008
    Oddometer:
    400
    Location:
    Chilly Northern Europe
    +1
    I'll soon tend to dig into religion on my carb problem. After 10000's of troublefree kms the idle suddenly went very rough with awful stalls, almost all last year's season without proper idle. Believe problem is too rich because idle is fine when cold and gets gradually worse when heating up. Always runs like a champ when throttled, just the idle is rough. Disassembled and cleaned and checked out everything twice, all hoses are new, new TPS. Still NO IMPROVEMENT AT ALL. I plan to dig through the carbs once more A THIRD TIME with microscope on every single f*cking nozzlehole, throttleshafts, diaphragms etc etc. About to toss my beloved SE on the city dump...WTF have I forgotten to check?

    I read somewhere: ....if the stalling started suddenly, check for blocked air jets. They are in the top of the carb under the air horn. The front one sometimes gets plugged with oil from the crank vent. I'll triplecheck the airjets next disassemble
    #22
  3. slackmeyer

    slackmeyer Don't mean sheeit. .

    Joined:
    Jul 23, 2007
    Oddometer:
    4,385
    Location:
    Berzerkeley, CA

    Hah. Well, it's some comfort to not be alone. I'm more and more leaning towards diaphragms (vacuum pistons, as KTM calls them). But I thought I had seen you say you replaced yours in some of the research I was doing on old threads? A few years ago?

    #23
  4. zakou

    zakou Been here awhile

    Joined:
    Apr 2, 2003
    Oddometer:
    985
    Location:
    Almyros Magnisias, Greece
    same thoughts!!!! :)
    #24
  5. Head2Wind

    Head2Wind MotorcycleMayhem

    Joined:
    Mar 13, 2006
    Oddometer:
    2,702
    Location:
    NorthWet Washington
    Ride it!
    #25
  6. zakou

    zakou Been here awhile

    Joined:
    Apr 2, 2003
    Oddometer:
    985
    Location:
    Almyros Magnisias, Greece
    You are right !! :) Its just the fact that I visit all these countries around the Balkans that makes me think about possible problems that may arise ! I have 2005 950 Adventure with 60K km .
    #26
  7. Balsta

    Balsta Been here awhile

    Joined:
    Feb 11, 2008
    Oddometer:
    400
    Location:
    Chilly Northern Europe
    ...Wish I was a carb magician like H2W and I would be riding with the normal SE-smile just some hours after the carb(s) went south instead of the frustrating "keeping the motor alive by using the foot brake pedal with messy throttling and jerking the clutch"...during almost one year now :ear:ear:eargetting used to it too like its the way its supposed to be:puke1
    #27
  8. Head2Wind

    Head2Wind MotorcycleMayhem

    Joined:
    Mar 13, 2006
    Oddometer:
    2,702
    Location:
    NorthWet Washington
    I understand the frustration and honestly it makes the 950 even more of a beast to ride when it isn't running the best that it can..... It was the driving force for me to solve it on my first 950. I recognized that the machine could be amazing if ONLY IT RAN RIGHT!

    I have a spare set of carbs that can be jetted to your setup..... :deal
    #28
  9. StevenD

    StevenD Hmmmm, dirt!

    Joined:
    Aug 3, 2005
    Oddometer:
    1,511
    Location:
    Holland, Amserdammed
    I have a good set of carbs left in northern Europe. :)

    Verstuurd vanaf mijn LG-D802 met Tapatalk
    #29
  10. slackmeyer

    slackmeyer Don't mean sheeit. .

    Joined:
    Jul 23, 2007
    Oddometer:
    4,385
    Location:
    Berzerkeley, CA
    I'm very glad that I can provide some resolution to this thread: My problems were from the diaphragms (vacuum pistons). I suspected the diaphragms, but I went ahead and bought a complete set of carbs from another inmate, because I just wanted the thing fixed. But I wouldn't be able to sleep at night without knowing what the problem was, so as soon as I received the new carbs, I swapped the newer diaphragms into my carbs. It completely changed the bike, it revs up smoothly, the slides start moving the instant the throttle is touched, and there's no more hesitation or backfiring.

    The difference in the flexibility of the diaphragm was pretty obvious when comparing new(er) and old side by side. But it's not like the old one was dried out or cracking- it just feels like it's thicker, slightly stiffer rubber.

    I get the feeling that this may be also responsible for the better and better gas mileage I've been getting in the last couple years, I've been creeping closer to 40 mpg on highway legs. . . .

    So now I have to decide if I'm going to buy new diaphragms for my carbs and sell the nice low mile set I just got. . . .
    #30
  11. RedRupert

    RedRupert Brit in the Soviet Union

    Joined:
    Jun 12, 2006
    Oddometer:
    809
    Location:
    Riga, Latvia / Bergerac, France / Colchester, UK
    Thanks for sharing this info with us. Something to keep in mind now that these 950s are getting pretty old. I have noticed that carb cleaner swells the diaphragms, so perhaps it's best to clean them with petrol/gas.

    Cheers.


    .
    #31
  12. Orange Toaster

    Orange Toaster Been here awhile

    Joined:
    Nov 8, 2008
    Oddometer:
    117
    Location:
    Copenhagen, Denmark
    So to be clear - your bike has no backfire or popping on decel at all now?
    snd all you did was replacing diaphragms?

    OT
    #32
  13. Dave1021

    Dave1021 n00b

    Joined:
    Jan 5, 2014
    Oddometer:
    1
    I've had a splutter at around 5-6k and have just cleaned the carbs. When replacing the front diaphragm it was to big to sit back in properly. I tried to clean them with carb cleaner first!
    #33
    econwatch likes this.
  14. slackmeyer

    slackmeyer Don't mean sheeit. .

    Joined:
    Jul 23, 2007
    Oddometer:
    4,385
    Location:
    Berzerkeley, CA
    No backfire. A small amount of decel popping remains, but nothing like what it was, and it's not any detriment to the way the bike runs (IMHO). I haven't had any more time to play with it since I posted. Before replacing the diaphragms, I had the bike set up on the rich side: 45 pilots, 165/170 mains, to try to solve the lean area at part throttle. I didn't change any settings when I replaced diaphragms, and there was a dramatic difference.

    If I was going to keep the stock airbox I'd change the jetting back to 42 pilots, 170 mains, but I got a air filter plate when I bought the low mileage carbs, and I'm going to try that out.
    #34
  15. ABuck99

    ABuck99 0.0

    Joined:
    Feb 21, 2009
    Oddometer:
    791
    Location:
    Georgia
    Does anyone have an idea what the parts list is in this rebuild kit? What do we get for $175 :eek1? Gaskets only? diaphragms, Orings? Float Needles?

    While I was inside the carbs last week, I noticed that my float needles had step or slight ring worn into the rubber tip- basically where it seats into the carb. Not having replacement, I buttoned it back up. But wondering if that is normal- or they should be absolutely symmetrical. What running conditions/behaviors could we expect from worn float needle?

    06 950 with roughly 26,000 miles

    Thanks
    #35
  16. Head2Wind

    Head2Wind MotorcycleMayhem

    Joined:
    Mar 13, 2006
    Oddometer:
    2,702
    Location:
    NorthWet Washington
    #36
  17. ABuck99

    ABuck99 0.0

    Joined:
    Feb 21, 2009
    Oddometer:
    791
    Location:
    Georgia
    Thanks for the reply. Seems not too many folks have purchased the rebuild kit- it's pricey. Hard to pull the trigger on that sort of $$ with out knowing what your getting. (similar to our new unaffordable health care program - you have to buy it to see whats in it...:lol3 ) Im thinking replacement valve needles- might be in order, at the least to have on hand. Bowls dont feel to be leaking - but the needle/valve I pulled had a noticeable groove worn in it.


    #37
  18. hotrdd

    hotrdd Been here awhile

    Joined:
    Jan 27, 2014
    Oddometer:
    174
    Location:
    Calgary, Alberta
    So I haven’t even picked up my KTM 950 S yet. But thought I'd start reading.

    I’m NOT a carb guru but there are a few things that I’ve learned from years of wrenching on my 1976 custom XS650.

    1) If you are experiencing popping or backfiring it can be more than just the carbs. You need to take into consideration and valve adjustment, exhaust changes or the fact that any of that emissions stuff is starting to get in the way. If you have a catalytic converter is there a chance it’s now getting clogged.

    2) The engine runs, on fuel, air and fire. If there is a chance you’ve changed the input or output of the fuel or air then you’ve already changed whether the engine is rich or lean.

    3) A good way to test for a seal leak it to just spray some carb cleaner or starter fluid around the carbs seals and boots and see if the idle changes.

    4) On the diaphragms if you think they are starting to get hard try soaking them in some 303 Aerospace. I LOVE THIS STUFF. Throw the “Armor All” out of your garage and replace it with this stuff. I use it on everything and have had some great success breathing life back into old rubber parts that are starting to harden.

    5) If in doubt do what I did and buy a set of Wide Band O2 gauges, they make it a lot easier to dial thing in and understand what is really happening. I picked up a double set of Amazon for around $380 http://www.innovatemotorsports.com/products/MTXL.php

    It would be awesome if someone could write a Carb Guide, with pictures, for those of use that don’t know these carbs.
    - What are the default factory settings?
    - When measuring float height what are we measuring off of?
    - What’s the best way to Synch them. Can I use my fluid manometer?
    #38
  19. Chuckracer

    Chuckracer Jerkus Maximus

    Joined:
    Aug 26, 2007
    Oddometer:
    10,337
    Location:
    Dexter, NY
  20. rattis

    rattis Long timer

    Joined:
    Apr 3, 2010
    Oddometer:
    3,953
    Location:
    East of the seas of Kattegat
    What's the size of those little o-rings on the inlet?
    #40