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Across breaks down at high rpm

Discussion in 'Technical and Troubleshooting Torque' started by scottay, Apr 23, 2014.

  1. Bike has had new plugs - New air filter - New throttle slides - Carbies had been balanced but it still breaks down in high rpm. One thing i have noticed is if im riding down hill the bike will rev to about 14k rpm before it breaks down. But if im going up a hill it will only get to about 10-11k rpm. It will literally just get to a spot and it wont rev past it.

    What could the problem be that would change with the angle the bikes on ?

  2. float levels?
    • Agree Agree x 1
  3. Did problem exist before the new parts were fitted or did you replace the parts in order to fix the problem. Did it start all of a sudden one day, or has it always done it since purchase?

    Throttle slides may not have been fitted correctly, ie diaphragm slipped out etc. Main jets may be partially restricted. Slide needles not fitted correctly, washers put above clip instead of below. Mud wasp nest in exhaust. Weak spark / ignition system problem. Restricted airbox inlet.
    • Agree Agree x 1
  4. Yeah the problem was there prior. I had a motorbike mech fit the slides so i wouldnt stuff it up.. Id hope he did it properly lol.
    its doing my head in. :(
  5. if it gets to a spot and won't rev past.. and that spot is higher downhill than uphill, then sounds like the power is being limited by fuel flow. downhill just requires less power than uphill, so revs higher at smaller throttle. spark breakdown at certain power level? I'd be looking at fuel first..

    Check Tinkerers suggestions... and look for other simple shit like kinked hoses, blocked filters..
    maybe the previous owner(s) "tuned it".. and the jets/needles are not good? can you check that they are to spec or suitable?

    go from tank to engine...
    tank got shit in it?
    fuel tap corroded/blocked/dead?
    fuel hose/filter kinked?
    inlet to carbs blocked?
    float needles stuck/way too low?
    jets, needles etc etc?
  6. Ill check as much as I can. Sadly im new to carbies and have no idea wtf is going on. Give me a car anyday to work on lol.
  7. The other thing ive noticed is when i start the bike it makes a tick tick tick tick noise from the fuelpump and then stops. I assume its priming.. is that normal?
  8. #8 oldcorollas, Apr 23, 2014
    Last edited: Apr 23, 2014
    apparently normal.

    bike carbs are not that different from car carbs.. ok, they are different, but same principle applies.. if it's clogged with crap, it's not going to work properly

    random ideas

    and more with the slider holders http://suzukiacross.org/2010/04/18/...unter-with-the-fallen-throttle-slide-holders/

    you'd hope they are in ok.. but it might be something else... and I'm outa wine for the evening :D (and I'm just guessing.. :chicken: )
    • Like Like x 1
  9. Ill have a look at those links thanks :)
    And i have no idea about car carbies either. They were a bit before my time haha
  10. Also does anyone know how i access the petcock with getting fuel everywhere ? lol

    And where is the fuel filter?
  11. do you have a manual for it? Suzuki across . org has one

    for removing tank, manual says
    1) turn fuel cock to "off"
    2) remove fuel line
    3) put pan under fuel cock assembly, and turn to "Res" to drain fuel.
    4) remove petcock assembly

    ps, I don't know much about your bike, take any suggestions with huge grains of salt and scepticism ;)
  12. Did you set the plug gap right ? Sounds like the spark blowing out to me.
    Might need a new coil and leads too.

    I presume its CDI with a carby.
  13. The spark plugs were gapped to what the manual said.
    And yes your correct with it being cdi and carby.
    The leads looked to be in pretty good condition when i changed the plugs.
  14. Might be lean breakdown, I'd do another test with a half turn out of the mixture screw.
  15. or think about getting a carby kit and cleaning it right up.
  16. I have no idea how to adjust the mixture :( im a noob lol
  17. Could also be worn cam lobes, weak valve springs, weak spark (ignition coils going bad), bad crank sensor.... bad earth connection.

    I'd check the simple stuff like earth connections and ignition coils first....my bet is on the valve springs personally.
  18. I'm betting spark on this one. spark will break down under load.

    "how old are the plugs and are they gapped properly?", is the first questions you should be asking.

    Then I'd be checking the resistance on the plug caps and across the secondary of the coils.

    I'm betting you can't change the leads easily, but there are ways. google.
  19. Spark will break down under load at low engine speeds where the alternator isn't really making the juice yet. As revs and voltage increase, spark picks back up. Wrong conditions for spark issue imo.
  20. I've experienced it under load on a few vehicles now.