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Rough running 3rd Cylinder

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by Jez79, Jan 29, 2013.

  1. Hi All,

    Riding my 99 bandit 1200 and found lately i'm running very rough on cylinder 3.

    My plan from here is to check vacuum, plugs, ignition coils, clean carb, valve clearance and possibly carb balance.

    Does this sound like logical plan of eliminations?

    Thanks in advance! :)
  2. Are you sure it's only one cylinder failing?
    I'd go:
    fuel lines, plugs, cleaning particular carb #3, ignition coils, valves, the worst - compression test .(not sure if the sync would make a difference, and I doubt it could be only one out of sync)
  3. yeh cylinder 3 only warms up mildly, while others get HOT HOT, so this suggests a problem isolated to 3. From my knowledge if it were fuel line or ignition coils either all or a pair would fail at a time
  4. #4 mike8863, Jan 29, 2013
    Last edited: Jan 29, 2013
    Start simple...
    if cyl #3 only gets warm while the others get hot then its fair to assume that there's not much combustion taking place in that cylinder.
    Step 1. open the drain screw at the bottom of #3's carb....fuel or no fuel???
    Step 2. replace the spark plug in cyl #3 checking there is spark before fitting the plug in the cylinder

    No fuel....check fuel lines, remove and dismantle / clean, check and reset carb etc..
    No spark.... ( having already replaced plug )....plug cap, HT lead, coil, wiring etc
  5. sound advice! will check tonight. Just need to confirm in my manual which one is drain screw on carb..
  6. checked drain plugs, getting fuel. swapped plug 3 with 4 and 4 now runs cooler. for a second it sounded better, so went for test run and found it was still running rough. had thought maybe something foreign in tank like water etc so checked and found there is gunk in the petrol itself, maybe old fuel deposits? would this suggest, flushing petrol, fuel and carbs etc and running new fuel? at the same time i would replace the spark plug in question.

    what do you think?
  7. First thing you need to check is compression or better still do a cylinder leakage test. Leakage test if far more accurate and reliable and tell you if your valves or rings are leaking and by how much. Up to 10% is normal, up to 20% is poor and anything over that means you are wasting your time doing anything else until you fix what ever the cause is. If you cant do the test take it to someone how can, Dynobike would be a good place to start.
    Once you are confidant the engine is in good condition go through all the other possible s one by one as you have mentioned.
  8. It sounds like cleaning the fuel system and a installing new set of spark plugs would be a worthwhile excercise.
  9. Dedge - Yes, have been trying to get a compression tester, and wanting to do my valves anyway as she's due. Then I could put compression and valves to bed and start troubleshooting all the other possibilities..

    Looking at the fuel, I will definitely empty, flush, replace and blow out carbs while I'm at it. Will also double check all vacuum hoses..

    Would carb syncing be relevant in this case?
  10. If the fuel in the tank shows obvious signs of contamination then it has to go and cleaning all carbs and replacing fuel filter would be warranted.

    If swapping the plugs cyl 3 to 4 moves the problem, then it would be fair to assume that you have a crook or badly fouled plug.

    Have a look at all 4 plugs. If they are showing signs of age/ wear /being past the use by date then,

    lash out and buy a new set.

    NGK - JR9B are listed as the standard plugs for a '99 bandit 1200, DR9EIX the iridium options....
  11. another thing I just read to check is worn needle jets, will check tonight.. I have a Danmoto straight through can on it so I assume if i need to replace needle jets, i might as well just upgrade needles and jets with a dynojet kit yeh?
  12. Mike8863+1
    "If swapping the plugs cyl 3 to 4 moves the problem, then it would be fair to assume that you have a crook or badly fouled plug."

    If moving the plug moved the problem, its not compression or fuel or coils or the phase of the moon, its the plug.
  13. i would love to throw new plugs at it, but if plug is fouled and not just dodgy, i'd like to rectify why it got fouled. problem may have just migrated to cylinder 4 with the fouled plug. i'm thinking compression test, clean/inspect carbs, new fuel, clean plugs and retry?
  14. Just be careful taking to much from a compression test it's not reliable, a leakage test is the only way to accurately gauge how good the engine is without pulling it apart.

    From the problem you describe carb balancing is a waste of time. Carb balancing is performed on a service to adjust for general ware a tear, it has little effect on mixtures, and simply ensures all four butterflies are evenly matched when the throttle is open.
  15. try switching your coils over. the #3 coil could be gone.
  16. Wouldn't disagree with any of that as a nice way to treat your bike, but in the interests of getting mobile and also confirming or otherwise the diagnosis, I'd try a set of plugs first, see how it goes and then go through your list as required.
  17. Make it run on all four before you start mucking about with jet kits. If it's got a cylinder specific problem now, putting in a jet kit will just mean it has a cylinder specific problem and jetting you can't sort out because of the problem.

    First rule of troubleshooting and modification:

    Change only one variable at a time.
    • Like Like x 1
  18. Lash out and buy a new set of plugs...you cannot 'read' old plugs to determine rich/lean or oil fouling
  19. put new plugs in
    take for run
    take plugs out and compare
    the colour of the plugs give you a good indication of whats hapening including if its running too rich/lean, hot/cold and if there is oil in the picture

    quick google got me this link

    im sure there would be nicer pics out there, but this is a start
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