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900ss Here It Goes - 2nd Life... Or Not

Discussion in 'Supersport (1974-2007)' started by Alex Elle, Sep 20, 2020.

  1. HI Folks,
    as already mentioned https://www.ducatiforum.co.uk/threads/hello-from-the-city-of-villains.80703/ I attempting to restart the bike I inherited, after 7 year of being in a garage. Its a 93 900ss and I done the following to it in the last few month:

    slow strip down
    tank de-rust (rostio)
    new fuel pump / filter
    new belts
    new oil / filter
    new spark plugs
    new battery
    carbs strip down and replaced nearly all seals

    Result is this:

    So it looks like its misfiring on vert cylinder. I found a little split in the outer diameter of the diaphragm of the vert carb. I swapped it to the horizontal carb, but still no change. It does not hold idle and dies quickly. After a few attempts the heat goes up and if I wiggle on the gas it does not take anything. Maybe once/twice I managed to get above 2500rpm for a few sec but it just dies after letting go.

    I checked for spark as well and both cylinders have a small ignition.

    What do you guys think?

    Is it down to my carb strip down? What could I get wrong? I set the pilot screws back to the same distance as before (4.1mm), also the float has been left on the same height 10.8mm.

    Or electrics?

    Thanks for feedback,





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  2. From my own experience, electrical issues very often appear as fuelling issues would. I chased a running issue for a very long time, thinking it was fuelling when it was a dodgy brand new coil. The wiring and electrics are OLD and were never great anyway during Cagivas ownership. I love an electrical challenge and made my own main loom. Ive replaced all of the ignition system too. My point is, it could be a number of things, the wiring and ignition is certainly worth looking at, even replacing. The pickup coils break down and are a weak link at this age, the Kukosans sometimes go too.

    Sorry your video doesnt work my end, says its privat so Im just making suggestions. Try swapping the coils, and Kukosans round and see if problem moves.
  3. Thanks for that, yes I'm looking into the electrics...

    Video should work now...
  4. If you are happy with all fueling checks (you know about the small "O" ring that is revealed when the black plastic diaphragm cover is removed?) then as said, you could try swapping coils, exciter boxes, (BB1105) plugs, even plug leads and checking relevant wiring before looking at pick-up coils (and wiring for shorting-out and/or poor connection) in crankcase.
  5. Small O-ring has been replaced aswell
    What are the kukosans?
    Wiring on the crankcase is near the clutch right? Connecting to the footrest?

    Will have another go today, but need more fuel first
  6. "the kokusans" are the "exciter boxes" adjacent to the the coils marked BB1105 on them as std.

    Kokusan is the manufacturer..
  7. When you've identified the exciter boxes, (next to coils in your picture) you can follow the two braided wires on each box down to the crankcase where they disappear on route to the two ignition pick-ups* (on L/H side of engine).

    *item 35.

  8. FD29B58A-D751-4ED0-8840-D00ADAB1D9A7.png The float heights should be 14mm, if I’m reading your post correctly you have them set to 10.8mm, if I were you I’d reset the float heights next.

    You can check your fuel level in the bowls is correct by attaching a clear tube to the drain and checking that it aligns with the circular feature with the pin in the middle on the carb body ref the right hand side of this photo.
    Note, once you’ve put the pipe on the drain spigot undo the drain bolt very slowly to get an accurate reading in the pipe.
    #8 Mark9, Sep 21, 2020
    Last edited: Sep 21, 2020
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  9. Swapped around coils and exciter boxes (BB1105), with no improvement. Also wasn't able to measure the resistance of the coils.
    On HV circuit it states 3700 Ohm as std (I got nothing) and LV 0.34 Ohm as std (I got 4 Ohm). When I was checking for spark, I found that the coils will get hot if you run it for a bit.

    Thanks Mark.
    I measure the float height prior assembly like this:

    I done this just now and took a short video. I gently wedged the tube on the carb, so I got my hands free.

    LH Carb

    RH Carb:

    Between the videos I switched on the pump to make sure carbs are full. It feels like the float needs adjusting, as it appears to be still ~15-20mm far away from the feature you mentioned. Do you think moving the float by 2-3mm will lift the float when checked with a tube to the round feature you mentioned?

    Sprayed a bit of cold start into the carbs and it feels like it helped briefly, so I will pursuit fuel for now.

    Cheers guys (and gals)
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  10. I think I could see an air bubble in the tube, this will throw out the measurements, it sometimes takes a few attempts to get a good reading, try it again and move the pipe up and down to allow air bubbles to get out of the pipe, if you’re not sure of the reading close off the drain screw, pull the pipe off to empty it and start again, it’s a bit trial and error but once you’ve had the result repeat a couple of times you know it’s reading correctly, with the floats set at 10.8mm you should end up with too much fuel in the bowls, not too little, this is what makes me think you need to repeat a few times to get an accurate representation of the fuel level, 14mm float height is the correct setting with standard intake and exhaust (your measurement method is fine), if your running K&N’s and free flowing exhausts then maybe set to 12.5mm but that’s all trial and error .
  11. Evening all,
    I had some time to do a another check on the float level:
    IMG_20200924_194802.jpg RH
    IMG_20200924_200122.jpg LH
    Measure looks ok to me. This time I basicly pushed the air gently up again to avoid the air bubble in the tube, and closed the drain screw. I ran the fuel pump briefly to fill up on missing fuel(if it was the case). This method worked quite repeatedly and it felt ok. Still tells me I need to check the float height to ensure I state the correct thing.

    I remembered I found information here: https://www.litetek.co/Guide_Mikuni_BDST_Fuel_Level.html#Ducati
    When I checked my carbs I measured the same dimension, thats why I left it..

    Is it worth checking it 14mm float height works better?

    I remembered the chock needle in the carb was looking funny on one side. The fine needle end on the left. That chock does not settle as nicely as the other
    Anyone got some of those? I would want to replace it.

    Also I cleaned the other diaphragm (13). What does this circuit do ?
    Carbs is a bit like alchemy, right ?

    Thanks for any thoughts.


  12. I have a few sets of carbs and may be able to help with parts.
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  13. Hi Alex, you need to leave the drain screw open when checking the levels, regarding the 14mm float height this was recommended to me by Neil at Cornerspeed Ducati, he is always right:), also 14mm is widely accepted as the correct setting if you are using the standard air filter/box and exhaust.
  14. When I took the picture the screw was open. So reading should be right. I will strip it down anyway, might have still something clogged up...
    Maybe done a doggy job as I'm only a dodgy engineer
  15. Nothing wrong with dodgy engineers, I’m one, aerospace, hope you all still feel safe on your next flight;)
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  16. Had a look at float again last night and came to this video below. Once you push the float gently it goes even down to 8.5mm :astonished:

    So just to be clear when I just let the float drop onto the first position, is when it should be at 14mm?
    WSM is also not really clear on what level it should be...

    Also found that the pilot merge cavity still was not really clean and some more sorting required...

    Defo need one of those chocks, as the needle tip appears to be sort of melted...
    I send you a pm.

  17. Looks as though either the springs in the needle valves have weakened or become clogged with old fuel or debris, or the float pivot is jammed slightly or clogged, pull the pivot pins out and clean everything thoroughly, spraying carb cleaner into the needle valves whilst depressing the pins slightly sometimes clears them out and allows the pin to spring up adequately, often you need to replace the needle valves with new ones though, when checking the float heights the carb body’s should be held at 45 degrees so that the weight of the float just bears down on the pin in the needle valve, if they are sticking as yours are it’s either, weak spring in needle valve, contamination in needle valve stopping the pin springing up sufficiently, contamination in float pivot assembly, distortion of float assembly , once you’re sure the float assembly is pivoting freely and the needle valve pin is springing up correctly you should be able to repeat the float height setting process and find that the float will settle in one position consistently and not stick when manually depressed .
    PS also check that the float isn’t punctured and containing fuel (this would make it heavy and stop it floating correctly in the fuel in the bowl).
    #17 Mark9, Sep 29, 2020
    Last edited: Sep 29, 2020
  18. Sorry to interfere, but I have not been able to comment for a while as I am in and out of hospital ongoing, back in again tomorrow....:rolleyes:

    Are you measuring the right side of the floats?

    You should be measuring 14mm on the squarer of the two. 14mm is a start point for the 900ss, and the 750ss seems better at around 12.5mm.

    There is roughly 3mm difference between the heights of the two float elements (so I would leave yours alone if it used to run alright) and look for another problem.....the pilot circuit can be one of the main issues as it is easily blocked.

    Also, when you measure the heights, take the float bowl and turn it round so it sits with just two screws on the body where the float assembly is inserted. This stops the float assembly from flexing in the socket and O-ring.

    NB! When you are measuring float heights the carb body is effectively upside down, so the greater the dimension, the less fuel is in the float bowl when the right way up; so if you set a 14mm height on the smaller of the two float elements, you won't have enough fuel in the bowl.

    In addition, you don't say if you have a Dynojet kit fitted (or if you have, I didn't see it) but depending on which kit (Stage 1 or 2) or OEM needles and jets, the pilot screw adjustment is at least 2 turns difference; ie 2 turns out or 4 turns out for Stage 1 and Stage 2 respectively. The main needle clip should be on the fourth groove from the top in both cases.

    float measure.jpg
    #18 Arquebus, Sep 30, 2020
    Last edited: Sep 30, 2020
  19. Just found a bit time today.... So float needle were stuck and now got them all freely moving, adjusted the float height to 14mm. Cleared all the little passages and made sure no blockage. Slow progress...

    Had an issue with the chokes, one seal was split and the needle moved very heavy..
    Looks like, they need replacing. Does anyone know where to get them in Uk?
  20. not sure if i am right but someone on here will clarify it but think the carbs are the same as yamaha trx items so rebuild parts should fit but as said i am not sure other people on here know more on carby models than i
    but worth looking into
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