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RF900R - Spark and Fuel but not Starting

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by johnstonesa, Aug 23, 2009.

  1. A few weeks ago my RF900 started and spluttered on 3 cylinders. After checking plugs and plug leads, the bike then wouldn't start. I have taken the plugs out and cleaned them and tested them and they all have a spark present. Each plug was wet and fouled with fuel so I now presume there is fuel and spark getting to each cylinder. After pulling and cleaning and replacing each plug, the bike will fire a few times but not fully get going. My initial thought was a faulty coil or coils?
    Bike is '94 RF900R with 75,000km. Never had any issues previously, up until now it has been an excellent bike.
    Does anyone have any ideas? I am pulling my hair out at the moment with the bike lying in bits on the garage floor!!

  2. Knowing that family of engines pretty well and those carbies very well I'm betting you've got a float needle not seating properly.

    Does it clear at higher revs?
  3. Don't know. I can't even get the engine started at the moment. I checked the coils today and both are fine. My next thought is the spark plugs (they are 2 years old) or even maybe a couple of float needles stuck and flooding the engine, not allowing it to start! How might I check if the needle is not seated properly? Drain the fuel reservoirs on each carby?

    Any thoughts? thanks for your help!
  4. To get it started:

    No choke.

    Hold the starter button and slowly wind open the throttle.

    This will clear the excess fuel and get it to fire.

    It will also almost entirely confirms the float needle theory.
  5. I may still have the workshop manual for mine at home.
    Let me know if you want me to have a look.
    Failing that we could do a deal. I'd have another RF tomorrow :wink:
  6. no luck... only managed to get a few big backfires and no engine running.
  7. How did you test the plugs?

    You said the plugs worked fine then in a later post you said you checked the coils.

    If you tested the plugs in the bikes ignition system and they were sparking fine, the coils must be ok too.

    Contaminated fuel is a possibility.

    If you didn't do the plug/ignition check this way before; try this procedure, as it tests the ignition system as a whole:

    Remove the plugs, reinstall the HT leads to the plugs, earth the plugs to somewhere convenient on the engine, crank the Suzy over and look for a nice strong zappy spark at each plug.

    This test does not exclude gross ignition timing error. This is a possible, but not very likely cause.

    May the gods of diagnosis smile on your efforts.

    PS I'm assuming that RF900s have HT leads and that the coils don't plug directly on to the plugs. if this is the case plug the wired coils onto the plugs and go from there
  8. Thanks for the advice,

    I tested the coils with a multimeter and they are OK. There appears to be a good spark on the plugs but they need to be replaced so I'll do that first anyway. It feels like it is flooding itself as it seems to be trying to fire but can't quite get there! I've never has a contaminated fuel issue before but this could be a possibility also.