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Help Suzuki Across carb tuning

Discussion in 'Suzuki 250cc In-line 4's' started by laverdagraham, Oct 10, 2016.

  1. laverdagraham

    laverdagraham Active Member Premium Member

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    Hi all.
    Just wondering if anyone has had experience with setting up the twin throat CV carbs used on the Suzuki across. I did a thorough clean out and re-set the float levels in an attempt to get the beast to run properly. See the attached photo of the goo that was in one of the carbs, no wonder it was struggling.
    After balancing all 4 vacuum ports with gauges I borrowed from a friend, attention was turned to air mixture screws that were set at 2-1/2 turns out as a starting point.
    The bike will idle quite nicely, but has a massive flat spot off idle. Adjusting the air mixture screws does not really give much joy and finding the sweet spot for each screw is not easy. The bike is hard to start when hot, and I am starting to think that valve shims may need attention as well (we don't know the history of the bike). A test ride indicated that there is next to no power from idle to 5000 rpm and even then it runs out of puff before anything exciting happens. Any tips from forum members would be appreciated as we are keen to get this project on the road for summer.

    Cheers, Graham Carb clean.jpg
     
  2. bradley1977

    bradley1977 Active Member

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    How did the carb sliders look


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  3. laverdagraham

    laverdagraham Active Member Premium Member

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    Hi Bradley,
    Carb sliders were fine. I have a "donor" bike to raid for parts, and used 2 of the plastic slide holders that are renowned for wearing out. All ports have been cleaned and blown out with compressed air. The sliders (all 4) move freely and the diaphragms are in good condition. The biggest adjustment that we made from original settings was to synchronize the 4 vacuum gauges by adjusting the synchronizing screw in between the 2 carburetor bodies. This was originally a fair way out, but I assume that synchronizing was the right thing to do?
    Cheers, Graham
     
  4. bradley1977

    bradley1977 Active Member

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    Valve adjustment could be in order if having troubles when warm may also have a fuel starvation issues the filter is in tank kiffsta on this forum is a ace with the accords known issues


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  5. bradley1977

    bradley1977 Active Member

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    Across sorry


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  6. laverdagraham

    laverdagraham Active Member Premium Member

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    Kiffsta is the one who alerted me to the slide holders that wear out. :D
     
  7. bradley1977

    bradley1977 Active Member

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    Is fuel pump running


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  8. laverdagraham

    laverdagraham Active Member Premium Member

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    Fuel pump runs OK I thimk. Builds pressure then stops, then gives smaller "pulses" to maintain pressure as fuel is used.
    Graham.
     
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  9. bradley1977

    bradley1977 Active Member

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    Hmmm I'd suggest valve clearances as a rule out measure


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  10. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    the manual does say 1.5 turns out

    across.PNG
     
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  11. laverdagraham

    laverdagraham Active Member Premium Member

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    I just downloaded a manual from the 250 forum after joining as a premium member. Now I have some good specs to help out might make some more sense. Starting at 1-1/2 turns pre-set might make some difference now. Thank's for the tip.
    Graham.
     
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  12. laverdagraham

    laverdagraham Active Member Premium Member

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    Carbs all balanced and air mixture screws at 1-1/2 turns from start. Bike runs but "hunts" up & down in revs. When hot, it will only fire up with the choke on???? Any tips guys? I'm thinking this weekend might be valve clearance checks.
    Graham
     
  13. bradley1977

    bradley1977 Active Member

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    Rubber boots on carbs are tight to head? Personally my screws are out about 2 turns and the needles are on the second groove I use full Choke when cold for a min then turn straight off, leads all good ? I personallly suggest clearances and possible compression test but I stand to be corrected


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  14. laverdagraham

    laverdagraham Active Member Premium Member

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    I just sprayed some CRC around the intake boots and idle improved a fair bit. You might be onto something with intake leaks Bradley, I think we will pull the carbs again on the weekend and ensure that they seal properly. As the rubbers are pretty hard, I might look at something to assist with sealing. Maybe a rubber grease or similar.
    Graham
     
  15. GreyImport

    GreyImport Administrator Staff Member The Big Cheese Contributing Member

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    Most of the cracks u cant see till u bend them .... silicone them over

    I use rubber grease on the internal area where the carbs slip in

    intake rubbers.jpg
     
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  16. laverdagraham

    laverdagraham Active Member Premium Member

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    Now there's a tip! Thanks Greyimport. :thumb_ups:
     
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  17. bradley1977

    bradley1977 Active Member

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    Brake cleaner works a treat to find vac leaks
    It def sounds like a lean mixture problem
    Mine has done 72000 and has no compression probs so hopefully yours doesn't


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  18. laverdagraham

    laverdagraham Active Member Premium Member

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    Wow, 72k and still going. What is your maintenance regime? Oil changes, plugs, tune, shims etc. I didn't realize that long life was also a feature of the Across.
    Graham
     
  19. bradley1977

    bradley1977 Active Member

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    Valves every 15 oil every 5 with filter and plugs every 30 and use motul oil
    Doesn't rattle doesn't smoke starts first time every time but sadly it has been replaced by another bike


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  20. bradley1977

    bradley1977 Active Member

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    How did you get on graham ?


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