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Project Suzuki GSX 250

Discussion in 'Your 250cc Projects' started by MarcusG, Nov 12, 2016.

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  1. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    CV's will never run right with pods because of air turbulence. An airbox is correctly called a still-air box or an air-resovoir as there is little turbulence inside them. Velocity stacks used for tuning intake length also reduce air turbulence inside the airbox itself

    It's all about volumetric efficiency... as the engine spins faster, it uses more of the air available and creates low pressure (vacuum) . But the airbox cannot always be replenished as fast as it is drained, so you get a drop on volumetric efficiency and a low pressure zone inside the airbox. So a bigger airbox might actually be better, if only to slightly reduce the drop in efficiency.

    I read somewhere that a general rule of thumb for tuning is that the total volume (meaning air/fluid volume, not how loud it is) of the intake system should match the total volume of the exhaust system. If you think about it, putting a shorty exhaust or ditching the airbox and running pods compromises on this and usually results in poorer performance except at peak power.

    Now look at ram air systems. They work by reducing the drop in pressure inside the airbox, which helps maintain volumetric efficiency. The long air tubes act like velocity stacks or runners, smoothing out the air and reducing turbulence. As you can imagine, the faster you go, the better this effect works (to a point). You will never get the airbox pressurised above atmospheric pressure with ram-air though. To get 100% efficiency or above you need forced induction.

    There is a reason every manufacturer of sports bikes uses a ram-air system. Because it works. My GSXR has air solenoid valves and air jets, that open at certain RPM's and throttle openings but that's a whole other can of worms to open up. Suffice to say it works by slightly leaning out the mixture.

    So instead of dicking about with pod filters, we should be looking at fitting a bigger volume airbox and/or creating our own ram-air systems. This way we might get some actual gains, instead of trying to mitigate losses from pods :thumb_ups:
     
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    Linkin, Nov 16, 2016
    #21
  2. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Linkin, Nov 16, 2016
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  3. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    Good read, although I got a bit lost with section 1 of the theory.
     
    Murdo, Nov 16, 2016
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  4. MarcusG

    MarcusG Meds

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    I just read Bens entire project thread and feel as though I have lived another life. A lot of great lessons in there that I'll no doubt reference back to.
     
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    MarcusG, Nov 16, 2016
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  5. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    Take the filter out of your stock airbox and see how fast it goes. Even with a stock airbox your filter might be too restrictive.
     
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    Frankster, Nov 16, 2016
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  6. Johnny

    Johnny Well-Known Member Premium Member

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    It would eventually kill the engine, I suppose. My bike ran already lean, so I replaced those rubber boots (and the O-rings inside of them) on both sides of the carburetors, and it made the bike run so much better, much smoother! The old boots were cracked and letting excessive air in. But I am pretty sure that the bike needs at least a top-end(ish) rebuild (the left side smokes, burns oil), so my problem is more like already a too worned engine.
     
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    Johnny, Nov 17, 2016
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  7. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    Yes, the filter is only a small part of a bigger picture. It sounds like your bike needs new rings and maybe hone the bores while you have the pistons out. Maybe check your valve clearances before doing anything major. When I first started out, people would tell me to check valve clearances. I never did because I wasn't sure how to do it. Big mistake on my part. Hindsight is a wonderful thing. These days, whenever I'm diagnosing an engine, I do a compression test followed by a leakdown test and then go from there. Those 2 tests will give you a pretty clear indication of what is or isn't going on in your engine. Saves a lot of guess work and wasted time (& often money too).
     
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    Frankster, Nov 17, 2016
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  8. Johnny

    Johnny Well-Known Member Premium Member

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    Thank you for the recommendations! The valve clearances are set though, did them only a couple thousand km-s ago.
     
    Johnny, Nov 18, 2016
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  9. MarcusG

    MarcusG Meds

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    Update.

    Over the week end I finally disassembled my BS30SS Carbs.. Discoveries were:
    • It's jet set up is all stock except for the main jet being 130.. Big jump from the stock main of 117.5.
    • Carb was relatively clean.. until i tried to remove the needle jets from broth L & R carbs (photo attached).. There was so much gunk built up between the outside casing of the need jet and the carburetor body that it was acting like a grout or mortar bonding the piece to the carb body... To remove I used a generous amount of lubricant and delicate tapping with a hammer & rubber damper to prevent impacts from damaging the jet. You can see from the photo how bad the build up was.
    Going forward I am going to clean the existing jets, buy new float bowl gaskets online (if I can find them, parts seem very sparse for the BS30SS) or just cut a new set out of gasket paper, dip the carb body and clean, before throwing it all back together with new main jets (I've got size 125 and 120 main jets handy).

    The first set up I am going to try will be:
    Main: 125
    Needle: 3rd groove (stock)
    Pilot: 17.5 (Stock)
    Air: 132.5 (Stock)
    Pod: Uni-filter road pods (foam) - Photo attached on this, I haven't seen many use these.

    If the bikes still a bit sluggish at full throttle I'll drop to 120 main and see if there is a difference.

    Question I have:
    Does anyone have any tricks of the trade for cleaning old copper jets? There seems to be a few methods available. To date I've just brushed away particles using warm water, white vinegar and an old tooth brush, though there are still thin trace amounts of build up that I cannot remove. I am concerned that small abrasive deposits of the jets will hasten future built up and leave me with the exact same problem as soon as I leave the bike in the garage for longer than 2 weeks.
     

    Attached Files:

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    MarcusG, Dec 13, 2016
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  10. MarcusG

    MarcusG Meds

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    Also, these pods have a much better diameter. Disclaimer... I did attempt the air box conversion.. Though I couldn't source all the air box parts for it and I am missing the attachment tabs for it on the frame of my bike... I am only trying to get the bike running above average and reliably so that I can comfortably ride around town.
     

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    MarcusG, Dec 13, 2016
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  11. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    With the main jetting, you may even need to go smaller than the original 117.5 main jet's, the foam filter's let more air though, which draw's more fuel through, i've seen it happen quite a few time's.
    Make sure you use foam filter oil on the new pod filter's too, i use Castrol filter oil (around $12 from Supercheap etc)

    [​IMG]




    Soak the jet's etc in Threebond Super Engine Conditioner, or Yamalube Carburetor Cleaner Dip, they'll come out looking new.
    Repco sell the Threebond for about $14 for a 240ml tin
    [​IMG]

    Or Yamaha dealer's sell the Yamalube Carburetor dip for around $23 for 940ml's and you dilute it (make's about 3 Litres)

    [​IMG]
     
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    my67xr, Dec 13, 2016
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  12. MarcusG

    MarcusG Meds

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    Mate that was quick. Much appreciated I'll get down to repco!
     
    MarcusG, Dec 13, 2016
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  13. Frankster

    Frankster Grey Pride...Adventure before Dementia Staff Member Premium Member Ride and Events Crew

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    Quick questions...when you open up the air intake, shouldn't you go to slightly bigger main jets? If you go smaller, won't that cause the engine to run lean?
     
    Frankster, Dec 13, 2016
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  14. Murdo

    Murdo The Good Doctor Staff Member Contributing Member Ride and Events Crew

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    Threebond the jets and carbs.
    Foam filters will hopefully flow a but more air than the silly pod things. You may find that to get the CV carbs to run smooth will need to have longer intakes to filters. Jetting will be a trial and error (terror) to find what works.
    Always run the carbs dry if you are going to leave bike for a week or more. (I turn the fuel tap off about a block from home and let the bike idle in driveway until it stalls.Next time just turn fuel on before you check oil and it should be ready to go.)
     
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    Murdo, Dec 13, 2016
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  15. MarcusG

    MarcusG Meds

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    I messaged @Brendengra on the intake filters. He added k&n pods & a 50mm rubber extension from the carburetors to help with airflow and apparently has it running running almost perfect. I'll copy and get the same extension.

    The annoying thing about the fuel cock on this bike is that there is no off.. There is "prime" or "on". There is a vacuum line and a fuel line running from the carb to the tank, so If i drain the carbs.. They will drain till the tank is empty. Do you think there is something wrong with the fuel cock here?
     
    MarcusG, Dec 13, 2016
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  16. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    If you leave the fuel tap on On and drain the bowls they wont refill till you turn the tap to prime, or if you try and start it they will slowly fill.
     
    my67xr, Dec 13, 2016
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  17. MarcusG

    MarcusG Meds

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    Okay, so fuel only flows through the bowls of the carb if the engines on? That will save me a tonne of effort.
     
    MarcusG, Dec 13, 2016
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  18. Brendengra

    Brendengra Active Member

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    I just disconnect the vacuum and keep bike going until completely empty. Easy as.
     
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    Brendengra, Dec 13, 2016
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  19. MarcusG

    MarcusG Meds

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    IMG_0482.JPG Hi all,

    Just a quick update on where I got to RE my carbs.

    Before Chrissy I disassembled the mikuni BS30SS, carb dipped the body and cleaned the jets with 3 bond engine conditioner as recommended which worked a treat. I found it really hard to find new gaskets for the float bowls so patiently made my own. Anyway, I threw it all back together in the following settings:

    Main: 120 (new)
    Needle: 3rd groove (stock)
    Pilot: 17.5 (stock)
    Air: 132.5 (stock)
    Pods: 50mm uni filter road pods (foam) with 50mm extension hoses to create some "travel" for the air as recommended.
    Mixture screws: 3 turns out from base

    I've been riding a bit over the last couple of weeks and the bike has so far been reliable. Throttle has good response at bottom and top end and the idle sounds nice around 1200rpm.

    Before I refurbed the carbs the bike would top out at about 100kms/h... It can now easily get it to 120km/h on a flat road but am not that keen in pushing it any further.

    Here's a photo of the final set up.. noting I am yet to re-wrap the ugly exhaust pipes. hopefully I don't get a lot more trouble for a while.

    Cheers for the advice to date ! Much appreciated.
     
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    MarcusG, Jan 4, 2017
    #39
  20. MarcusG

    MarcusG Meds

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    And with old things there is always the next problem!

    When attempting to drain my float bowls I noticed fuel would flow regardless of on/reserve position.. to make sure this had nothing to do with the carbs I pulled the hoses from the petcock.. fuel still drained straight from the tank so I could only reason that the petcock vacuum mechanism wasn't working properly.

    Anyway, I ordered a petcock repair kit for the off eBay and made an effort to clean up the whole piece. Here are some before / after photos for any1 who's interested. I actually haven't tested if this has fixed it yet...I'll fill it with fuel this arvo when it's a bit cooler and update.

    IMG_0599.JPG

    IMG_0600.JPG

    IMG_0603.JPG


    And after:

    IMG_0606.JPG

    IMG_0608.JPG

    IMG_0610.JPG
     
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    MarcusG, Jan 21, 2017
    #40
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