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3 spark plugs on holiday? or another theory

Discussion in 'Bling and Appearance' at netrider.net.au started by Ktulu, Aug 16, 2006.

  1. Hi guys, just want to know if something's possible...

    Backstory:

    Tonight filled up at Shell servo (don't know if I'll trust them again...). Filled up pretty darn full now that I think about it.

    Rode for 15k's without incident.
    Switch bike off for 10 minutes, ready to leave mate's house again.
    Start bike - bike dies straight away.
    I figure it's somehow flooded (engine it still plenty warm), start it again and give it a good rev to clean out the 'whatever'.

    Bike comes good, we move off - suddenly bike is lagging badly. Like some cylinders are missing. It felt EXACTLY like when you start your bike and it's super cold and you twist the throttle a bit and it doesn't really respond, it just kind of bubbles towards higher revs, but doesn't want to get there (like me at about 5am... *am totally surprised the bike didn't tell me to f***-off and go back to sleep*).

    -Except while moving.
    So bike was super slow, I throttled off and it seemed to come good so I got back to catching up, but then bogged down again.

    Same thing happens until I can catch up with Laurie and Scrambles at the next set of lights - flip the visor and explain.
    We pull into a car-park, turn bike off. Start again and give it a good rev.

    More test revs, higher and higher. Seems fine.

    Ride on, no noticeable incidents from then on, and on the way home from the Ranch it was perfect.

    So I have 2 theories:

    - crappy fuel. Damn you Shell, ya damn damnity damned damndified vendors of crappy dungleaded.

    OR



    - by overfilling the tank, under acceleration the fuel was pushed back sealing off the cap, failing to allow a vacuum created by fuel being taken from the bottom to be alleviated by inflow of air. The vacuum caused fuel starvation to the engine, causing what I described.
    This would also fit with why it seemed to come back when I throttled off - fuel moves forward = cap can breath =, fuel not restricted.

    So apart from carrying on thinking I know everything and have adequately explained my problem using a word that has 2 'u's in a row in it [making me seem like a freakin' NASA scientist or sumfink], I figured I'd check the tome of knowledge that is Netrider.

    Is it likely I just overfilled the tank?
     
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  2. The question is did the bike smell like it was running obscenely rich when it was doing it's acting gimp thing?

    I once had an atrocious batch of petrol in my old FZR250 3LN-3, oddly enough also from Shell! It resulted in the bike running like an absolute pig until i managed to empty the tank and get some fresh juice.
    There's a few things it could have been... listing these from my experience with FZR's.

    1. Your EXUP valve is playing up and had jammed completely closed. If this is the case then it would have given similar symptoms as decribed - but more so a complete lack of power above 9k rpm. Check the EXUP valve and cables and make sure it has smooth and adequete movement.

    2. Carbs are gummed up and one of the slides got stuck open. This would've caused one cylinder to run pig rich and given similar symptoms. Time for a full carby strip down and clean.

    3. Spark plugs are fouled. Not quite the same symptoms as given, but it could also have been a loose spark lead. Remove them all, inspect for colour and condition... might want to clean them up (or buy new ones! they're only ~$4 each), then reinstall.

    Oh, and about your tank theory. It's unlikely... but you can check the overflow hose and the tank breather valve (in the petrol cap) to appease your curiosity if you like. :grin:

    PS. There's a heap and a half of info over on the FZR250 Forums.
     
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  3. Suck a bit of fuel out giving it some breathing room and see how the rest of the tank goes but sus fuel is on everyone's mind these days I'm thinking.
     
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  4. id agree with the suss fuel theory. Here's my take on it.

    The bike was ok when you left the servo as all the crap in the fuel was mixed throughout the tank. Once the fuel had time to settle down, all the crap from the bowser settled to the bottom where your fuel pickup was.
     
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  5. hmmm, I think I'll just fang my way through this tank of fuel as quick as possible and see how it goes.

    Cheers guys!
     
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  6. tank theory not likely, fuel upon agitation expands therefore it would not need to breath THAT much to fill your carby in order to run correctly.
    that said, a completely blocked breather and minimal fuel MAY cause what you say. think, more fuel=more expansion=more pressure, less fuel=less expansion=less pressure.

    i would think carby's or plugs OR plug leads!!
    maybe a bung lead causing intermittent fault, worth a look anyway.
     
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