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Backfires on startup

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by CamKawa, Jul 28, 2005.

  1. Picture this, it's 11:30pm at night, I quietly shuffle out to the bike and put on my helmet and gloves. I open the choke and press the start button then BANG! The whole neighborhood is awake. :D
    I recently changed the plugs and cleaned and re-oiled the oil filter on my 2002 ZX9. When I re-oiled the air filter I didn't hold back on the oil and soaked it right through then pressed it into a towel to soak up the excess oil. My question is could I have over oiled the filter making the bike run too rich causing a backfire on startup?

  2. HAAAAHAHAHAHA, thats awesome i'm gotta do that to someone
  3. I'd say more likely one or more plug isn't firing on startup, and raw fuel is passing through into the exhaust pipe which then ignites with a bang when hot exhaust gets through.

    Check all your leads, then if necessary, check things like spark plug gaps, maybe even replace em again.

    That would be my thoughts, but then would would i know, I'm just a noob to bikes.

    (But having 10 years engineering experience, i know a little about motors. ;) )
  4. did you end up riding the bike? did it run normally?

    my guess is you put the leads in the wrong way ;)

    about the air filter, dont put too much oil on it and let it
    sit for a LONG time (at least overnight) before you put it
    back in.
  5. I agree with Androo, sounds like you got the plug leads around the wrong way. It can be easy to mess up cylinders 2 and 3. If it was running to rich because of the air filter you would start to be blowing out black exhaust gases.
  6. The bike runs ok once started and warm starts start without a bang. I'll check the plugs on the weekend if I find some time. The bike doesn't have leads so to speak it has stick coils with ignition wire clip things. Are stick coils cylinder specific? I’ll know this when I pull the bike apart, but does anyone know off the top of there head if the coils are cylinder numbered?
  7. not sure how dizzy's (distributers- gives the timed spark to a specific lead which then goes to a specific cylinder) work on bikes, but they are numbered and you do have to make sure they are set up right. around the dizzy or the cap it will have spark order, and on your block the pistons will be numbered, if you can't find it you'll need to grab an owners/service manual and suss it out. check if your pistons are covered in carbon (the black shit) then at least you'll know if your mixture and fireing order is ok. if your not sure man, grab a mate just so you can get a bit of hands on advice, and that way when you fcuk up and you got someone to blame


    If once it started and warms up you say it runs ok? runs good?

    if its the engine is jumpin round a lot more then its safe to say that you've probs got the firing order wrong,
    I'm not a bike mechanic and i've never worked on a bike because i don't have one yet. not sure if i bike will run with wrong firing order. have some knowledge of cars which is where my limited knowledge of this subject comes from
  8. Bikes and modern day car engines don't use distributors. They use coil packs! Whether they are mounted on the frame or directly on the spark lead doesn't make any difference. They get there timing from pick up points on the crankshaft so they need to fire in sequence. The bike will run if they are around the wrong way but will run roughly. It can cause a back fire on start up as the computer will be enrichening the fuel air mix for ease of starting. You may not notice it running roughy until you open it up and would start to break down at high revs. The leads should be marked somewhere what cylinder they belong to and number one cylinder should be on the outside right hand cylinder, the one that sits against you right knee. I would be making it a priority to check these leads before riding again as it can further damage your engine.

    FYI Commodores from VN upwards used coil packs and my XTrail uses coil packs on the end of the spark leads.

  9. how do they work? ...my thoughts of my knowledge just got a lot smaller,

    does make sense tho, electronic timing...
  10. Hey, you should be happy.....you've developed your own "big bang" engine :LOL: :LOL: :LOL: :LOL:

    All the motogp teams paid big bucks to develop that type of engine and you did it all by yourself... :p
  11. I'm still thinking spark plug gaps.

    I remember dropping a plug once when i was doing my car, and it landed, sparking end down. I didn't realise, but the gap actually about a quarter of what it should have been. It looked okay, there was still a gap.

    I put it back in and it was a biatch to start, ran like shite until it warmed up. Then it was okay.
    Warm plugs and engines will ignite the fuel easier thats why it will start and run better when warm, regardless of the plug gap.

    In cases you don't know:
    The 'gap' is the space between the point in the middle of the fat end, and the bent bit of metal coming off the bottom. It should be around 2mm but check your manual for specific gap size, it is important to get the right gap.
  12. I'd be checking.....

    .... to see if your Big Bang has started a new life form, you could end up being famous!!!!!
    (does sound like firing order, or an over-rich startup and raw fuel in the headers)