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Project '98 Suzuki Across

Discussion in 'Your 250cc Projects' started by Laceysnr, Aug 8, 2019.

  1. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    LEGEND , now to tune it :thumb_ups:


    I used to do a basic clean of a carb by doing pilot and main jets and emulsion tubes and 9/10 were good, however the passages between the slow air jet , pilot jet and AF screw could blocked.

    I am worried that you are at 2.5 turns out and it is now running and still sounds lean, to me taking the mixtures out another full turn is possible masking another issue. As these carbs sat for ages, you could have a blocked passage. CV carbs are cool, but can be touchy, 1/8 of a turn could be the difference between a good and bad tune , so having to go 1 full turn out to get it to run is odd.

    This diagram shows how the passage is routed between the airjet, pilot jet and AF mix screws


    carb1.PNG

    If you look at the slow air jet, it feeds air down a passage that connects with your pilot jet and the air fuel mix screw . I used Threebond engine conditioner to clean carbs and I now always remove the slow jet and the AF mix screw and spray threebond down the AF mix hole, it should bubble out the slow jet passage, when it does I block the pilot jet hole with my finger and I then should see Threebond coming out the slow air jet hole on the front of the carb , if that works then you know that passage is clear.

    I spend alot of time getting bikes that have sat for ages and this method has helped me heaps.

    Have a look at this vid for a vocal explanation of how it works.



    this is probably the best guide that I ahve read on how to set your AF screws
    https://litetek.co/Guide_FuelScrews.html
     
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    Last edited: Aug 14, 2019 at 4:01 PM
  2. Jethalter

    Jethalter Active Member Premium Member

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    Sounds alright so far,
    First thing would be to adjust the idle screw to get it to the point where its idling like the vid but with the choke fully off.
    From there then you would raise the rpm to 3k and balance the carbs and tweak the idle mix screws.
    Then see where your at.

    So far so good tho
     
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  3. Laceysnr

    Laceysnr Member Premium Member

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    Thanks for the input fellas. I'll have a crack at some more subtle tuning tonight. I was turning in pretty large increments just to find a run point. I blew compressed air in through the mix screw holes last night, and for each one could see a puff come out the front of the carb so pretty sure they're clear, but if I make no progress I'll strip it down again. Getting quite adept at getting them on/off now!
     
  4. Andych

    Andych Well-Known Member Premium Member

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    You should also look at the Needle settings.. if they are not right it can be very lean or very rich.. I cant remember the correct setting now...
     
  5. Laceysnr

    Laceysnr Member Premium Member

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    How do you adjust those? I've seen pictures showing the incremental changes you can make, and I get how they work by raising/lowering the needle relative to the slide, but when I had them out it wasn't at all obvious how you got to the parts inside of the slides and everybody seems to skip that! Maybe it's obvious but mine are just stuck together?
     
  6. Andych

    Andych Well-Known Member Premium Member

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    When you unclip each piston from the diaphragm you will see the little white hanger that sits inside the piston.
    Carefully pull that out of the piston and it gives you access to the needle clip.
    The higher the clip is the leaner the setting. I believe the setting factory setting should be the clip on the 3rd ring (approx halfway).
    The only reason I mention it is as per what @kiffsta said... with the mixture screws out that far it is way off what it should be..
    Doesnt hurt to double check as you really dont know what the PO has done.
    Could be they adjusted the heck out of the needles because them and the emulsion tubes are worn out making it run too rich on standard settings.

    Also make sure that the Bowl vents are free and not squashed or connected together... these are to the inside of each carby towards the air filter... you can detach them to double check... see page 187 of the Service Manual which shows all the hose routing.

    Lots of good info in this thread too....https://2fiftycc.com/index.php?threads/mikuni-bsw27-carburetter-rebuild-kit.919/
     
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    Last edited: Aug 14, 2019 at 5:48 PM
  7. Andych

    Andych Well-Known Member Premium Member

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  8. Laceysnr

    Laceysnr Member Premium Member

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    Yeah I read through that post before, wish it was that simple! That said, while I'm 99% sure I've blown air through those successfully, there's no harm in checking them again. WRT the screws, all the guides talk about revs increasing or dropping noticably as you tune them, is that still valid on a 4 cylinder machine?
     
  9. Laceysnr

    Laceysnr Member Premium Member

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    Checked the needles, they're still on the stock setting. Confirmed it's not the breather holes, if I briefly covered either one with a finger while running the revs would drop instantly, if I held my finger there for more than a fraction of a second it was enough for it to stall.

    There is a new development tonight though: when it starts it revs up to around 4000 on it's own really quickly and then back down. Definitely seems like a fuelling issue as without the screws turned way out it won't run, and if I give it any air it's the same deal. Either that or it's a leak between the carbys and the engine but spraying stuff around hasn't revealed any evidence of that.

    Fuel pump ticks away while the engine is running, exhaust is still spitting stuff out the bottom so definitely rich, but doesn't like to be backed off. Wondering if the fuel level is low in the bowls, so it has needs to compensate? Looks like I'm going to have to take the carbys off again at any rate!
     
  10. Jethalter

    Jethalter Active Member Premium Member

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    Is the pumping ticking fast or at a constant slow rate ?? fast pumping is empty bowls/low, slow is usually just to keep them topped up.

    I know my carbs on my across aint right, but its as close as i can get them at the moment without pulling my hair out and the carb in or out a dozen more times. What mins does is after not starting for a while, a month or so, it takes a few crank and dies for it to fire up(if its only a week or so it fires first try), after its started with full choke, cant touch throttle. After 30 secs or a minute it can rev up fine etc... my pilots keep blocking and its taking that long to clean them out. Once warm there is no issues, starts easy all the time, doesn't smell rich. I also get some condensation build up in the exhaust, which it burns out during warm up.
    One day i'll get around to converting it to efi.
     
  11. Laceysnr

    Laceysnr Member Premium Member

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    Starting to think an efi conversion would be easier, but as it turns out my petrol tank isn't as clean as I thought... Just pulled the hose to the carbys and got this:

    IMG_20190815_214413.jpg

    So i guess I'm going to have to get the tank out after all, which sucks. Where do I even dump the fuel that's in there? And yeah, moved the glass as soon as I realised I'd put it next to the extension cable!
     
  12. Jethalter

    Jethalter Active Member Premium Member

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    You didn't fill the tank with 'solo' instead of gasoline ????

    Problem i find is all the tanks are cactus for the most part, some form of corrosion, wasn't an issue on bikes 4-5 years old, but all these ones now that are 20-30 years old are kaput. The only proper way would be to cut open a section at the top to put in a big enough inspection cover so you could get right inside and clean. But more headaches.

    One day when i get around to EFI i'll do an aluminum tank too, so rust and stuff aint an issue ever.
     
  13. Laceysnr

    Laceysnr Member Premium Member

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    Yeah, I did a vinegar soak and stuff before but I think I need to get it off so I can shake it about and be more thorough. There's no lumps to block jets, but I can't imagine that stuff is burning as cleanly as it should so would need more of it.
     
  14. Jethalter

    Jethalter Active Member Premium Member

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    The pilots dont require chunky bits to block them up, just a little contamination of the fuel with say rust and it gums them up softly, which usually gets sucked clean after 30 secs/1 min. Remember the pilots are only 0.30mm holes, easy to block.
     
  15. Laceysnr

    Laceysnr Member Premium Member

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    That was a long few hours, felt like days!

    IMG_20190816_012031.jpg IMG_20190816_012020.jpg
     
  16. Jethalter

    Jethalter Active Member Premium Member

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    certainly not a fun job
     
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  17. kiffsta

    kiffsta Administrator Staff Member Dirty Wheel Club Contributing Member

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    Easy test for your tank is to pull the fuel line off your carb and put it into a clear bottle, then turn the key and the pump will do its thing , half fill the bottle and
    Check for junk in the fuel
     
  18. Laceysnr

    Laceysnr Member Premium Member

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    What's what the picture of the glass was above! There was more rust forming towards the neck of the tank where the fuel level had gone down which is why I decided to just get it out. I'll try and get it cleaned up and sealed now so that it should be good for a few years at least!
     
  19. Andych

    Andych Well-Known Member Premium Member

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    Dont put a liner in it... chances are it will fail. Talk to your local radiator shop about getting it cleaned up. I had the SRX tank done and they use a special chemical on it that stops flash rust forming.
    Easy enough to repaint the outside afterwards as it is just gloss black on the Across.
     
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  20. Laceysnr

    Laceysnr Member Premium Member

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