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Suzuki Across flat spot

Discussion in 'Suzuki 250cc In-line 4's' started by zook98, Mar 4, 2016.

  1. zook98

    zook98 Member

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    I've just recently purchased a 1998 Across, having been off bikes for many years. Two small issues;

    First is this morning the starter seems to have died. Fired up fine first thing, stopped for fuel round the corner, now starter does not engage. A faint 'tick' can be heard and lights dim a little when pressing starter button. Bike push started fine, battery is only a few weeks old. First start this morning it cranked strong.

    Second is a flat spot around 5-5500rpm. In any gear, winding on throttle from hear sees bike hesitate for a couple of seconds before it clears itself and then is strong all the way up from there. A mate riding with me mentioned some black smoke is visible at the same time, but is gone as revs increase. It also often needs some throttle kept up when slowing down to stop, or sometimes it will stall. Sounds to me like it is running a little rich.

    The previous owner modified the exhaust but shortening the original muffler by about 30% and re-welding the end back on. Is this a likely cause of the tune issue? He did also supply an original unmodified muffler.
     
  2. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    Hey Zook98

    I would check your starter solenoid , battery and starter motor and make sure the wiring is done up tightly and making good contact, another check you do is making sure your earth strap is properly grounded to the engine, all of these can contribute to the conditions you are seeing. Also the Across needs a really strong battery, even if its new if could be below par and causing your issues, this is a really good post on how to check things

    http://2fiftycc.com/index.php?threads/how-do-i-test-my-12-volt-battery-and-charging-system.1794/


    As for your black smoke, I would hazard a guess she might be running a tad rich, if your not confident with your carbs, drop it by a bike shop and get them to set them. Has the bike sat for a period ? Might be junk in the carbs.

    Let see some Pics of her - http://www.2fiftycc.com/index.php?showcase/

    Cheers
    Chris
     
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  3. Pygmygod

    Pygmygod Well-Known Member

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    Across definitely needs a strong battery with a high cranking amps capacity or she won't start.

    Flat spot around 5k rpm could be when it starts to get fuel via the main jet.

    I'd be cleaning out the carbs to make sure all the jets are clean/clear.

    If the exhaust is only shorter and not louder and not allowing additional airflow through it compared to the stock then it shouldn't make any difference.
    If however it's allowing additional airflow through it then you should be running lean, not rich.

    The pause in power probably means the fuel isn't being burnt and then when it finally gains power again it has some excess fuel in the exhaust which gets burnt up producing black smoke. Especially since your friend said he only saw it during this flat spot.

    Cleaning the carbs is the number one thing to do on old bikes. It's just annoying trying to remove the damn things from the bike, the actual carb cleaning process is pretty easy.
     
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  4. zook98

    zook98 Member

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    I've not played with the carbs on this bike yet, but they look to be a pain to remove. The exhaust is definitely louder than stock, but my thoughts were also that I figured it be running lean if anything. It's already had new plugs and filters done when I serviced it a couple weeks ago. Battery is still strong, testing with a multimeter is only seeing a voltage drop of about 0.2V when the starter is pressed.
     
  5. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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  6. Pygmygod

    Pygmygod Well-Known Member

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    Whilst your voltage may not be low you still require a battery with a reasonable amount of CCA (cold cranking amps) capacity otherwise it won't be strong enough of a kick on the starter to make the bike start.
     
  7. zook98

    zook98 Member

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    I would have thought if the battery was the issue, that a significant voltage drop would be observed when the starter is pressed?
     
  8. Pygmygod

    Pygmygod Well-Known Member

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    To make this easier. What battery have you installed?
     
  9. zook98

    zook98 Member

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    Update... Stripped fairings off and shorting terminals on the solenoid sees the starter turn the engine over. So new solenoid to go in.
     
  10. zook98

    zook98 Member

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    Ps, battery is VTX7A-BS, 12v, 150CCA, 6AH.

    Also what's the best way of getting carbs off? Looks like a shitty job!
     
  11. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    Undo the clamps that hold the airbox to the carbs, there are also 2 x 10mm bolts down wither side of the airbox that secure it to the frame. Once the airbox is out, then undo the 4 clamps that hold the carbs to the cylinder head, you will have to also undo the choke cables and the throttle cable to allow the carbs to come free. Once everything is undone, you can rock the carbs up and down free them from the carb boots.
     
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  12. zook98

    zook98 Member

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    Sweet got it. Actually was easier than I expected. Opened up the bowls and found a small quantity of a mud like substance in the bottom. Cleaned all that out and everything else has had a good flush out. How do I go about leaning it out a little?
     
  13. Linkin

    Linkin The Apprentice Premium Member Dirty Wheel Club Contributing Member

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    If you found brown crap in your carbs, then you need to replace your fuel filter... and also clean out and seal your fuel tank
     
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  14. zook98

    zook98 Member

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    Carbs pulled down, small amounts of same brown muck found around all main jets and in top caps. Diaphragms were a pain to get seated again properly.
    All I need now is a starter solenoid.
     
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  15. zook98

    zook98 Member

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    Found solenoid on ebay, so that should get me mobile again. Another point on this bike, I've had a small oil leak since I first picked it up, and I found it when I had the carbs off. On the rear of the barrels, there is a small flange with a blanking plate over it. The plate has a removable bung which looks like it's to give access to an adjustment screw inside. Can anyone tell me what it is? I didn't touch it, save for cleaning the housing and putting some sealant on an re-attaching the cover plate.
     
  16. wally_escondido

    wally_escondido Member

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    Hey Zook98, that's the cam-chain tensioner assembly (see attached?). They're non-adjustable on this bike, and the rubber bung is there to keep muck out. Perhaps the gasket between the assembly and the cylinder barrels has failed. While you've the carbs off, it'd be a perfect time to make a new one to replace it.
     

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  17. zook98

    zook98 Member

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    Well we're all up and running. Turns out the culprit was the clutch switch, so I've bypassed it till I can get a new one. Bike is definitely running sweeter, but still getting some light black smoke under heavy throttle. Do these carbs have mixture screws to enable leaning it out a little or is it necessary to pull carbs apart?
     
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  18. wally_escondido

    wally_escondido Member

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    The Across uses two Mikuni BSW-27 carbs which have pilot mixture screws just forward of the diaphragm caps. The factory setting is 1.5 turns out but this only affects the idle circuit. To meter and control A/F ratio at varying throttle openings, adjustments should be made to jet size and needle clip setting. Get in there, mate, hopefully you only have to reset the settings to standard in order to clean up your smoke issues.
     

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