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Project GSX250 restoration

Discussion in 'Your 250cc Projects' started by SwarleyAUS, Mar 21, 2017.

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  1. Alipture

    Alipture Active Member

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    I dont think anybody has said that. and it doesnt at 0 throttle because the needle is seated.
    You can idle lean (in fact a lot of bikes do it from factory) because the extra heat generated from being lean is pretty insignificant because youre not burning that much fuel

    Start with the main jet because thats the coarsest adjustment and affects the engine when its making maximum power.
    1/4 to 3/4 throttle both the main jet and the needle/seat both have an effect on fuel flow, at 3/4 to 1 the needle is no longer the main restriction.
     
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    Alipture, Jun 21, 2017
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  2. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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  3. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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  4. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    @GreyImport when i click on your link's like the one's above it open's it in a new tab, but i am not logged in on that page so say's download not available
     
    my67xr, Jun 21, 2017
    #204
  5. SwarleyAUS

    SwarleyAUS Well-Known Member

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    No I haven't seen that one, I'll have a read.

    Where I interpreted the fact that changing the mains effects the idle mixture:
    .

    I'll have a further play with the pilots so that it's not running lean, then adjust the mains if necessary. I'm doing it this way because the pilot jets deliver fuel throughout the rev range whereas the mains do not. Therefore any changes to the mains before pilots would necessitate then changing the mains again after the fact as the overall mixture has been affected by the pilots. I've read plenty saying to configure the jets the other way around, but I'm yet to see any rationale for doing it this way beyond 'to get the most top end power' - where I will never be operating.
     
    SwarleyAUS, Jun 21, 2017
    #205
  6. SwarleyAUS

    SwarleyAUS Well-Known Member

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    Ok so in the end I installed both the largest 22.5 pilot and 120 main that I currently have and got the best results thusfar I believe. Lessened hanging idle, quicker throttle response and no bogging at 5k.

    This is after changing the mains to 120's:

    https://www.facebook.com/video.php?v=10213634446874228


    And after changing the pilots to 22.5's:

    https://www.facebook.com/video.php?v=10213634466994731


    I don't dare rev it past 7k! Pretty sure I see an improvement with the larger pilot.

    Mixture screws are 1.5 turns out, but the plugs still don't have any (new) soot on them indicating I'm nowhere near to being rich. Guess I may yet need to go up a few sizes and play with the jet needle position... sigh.

    19401392_10213634448994281_977551124_o.jpg
     
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    SwarleyAUS, Jun 21, 2017
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  7. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    I reckon it might take a long time to build up any carbon on the plug's with it just idling
    Normally when you do a plug chop and check the colour of the porcelain,
    you put a slight load on the engine ( up a small gradient) in 4th or 5th gear at wot, then cut the engine, pull in the clutch and come to a stop, then pull the plug's out and check the colour's
     
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    my67xr, Jun 21, 2017
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  8. SwarleyAUS

    SwarleyAUS Well-Known Member

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    I was wondering if it might take some time.

    If I were to do that test, need it be in a high gear and if so why?
     
    SwarleyAUS, Jun 21, 2017
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  9. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    I guess you could try it in 3rd gear, most carby manufacturer's suggest tuning in higher gear's to get the engine temp's up a bit and also most people don't usually cruise around in 3rd or 4th gear
    What you need is the engine temp's up to normal running temperature, this will have the spark plug running at it's optimal self cleaning temperature
    With the correct main jetting it'll give you the best colour on the porcelain (light coffee colour)

    Main jetting come's into play from just below half throttle and, at 3/4 throttle the fuel/air mix from the needle is tapering off and the engine is pretty much running off the main jet to wot.
    You may never want to run your engine at wot but you still need the wot mixture's right so it's feeding the engine the correct amount of fuel from 1/2 throttle to 7/8 throttle
    On some hill's you need to be in a lower gear at higher rpm's to keep the power up, this is better than being in a higher gear with the engine revving lower and labouring, same sort of thing when you are trying to merge with traffic, or pass a slower car.
    The adjustable needle clip and needle jet is there for fine tuning the mixture's from 1/4 throttle to 3/4 throttle
    And the mixture screw is for tuning the idle to 1/4 throttle, adjustment here help's starting and will help get rid of hesitation's/stumble's when taking off, and give the carby smoother transition's between each circuit.

    So if you can blip the throttle without the engine hesitating the mixture screw is adjusted and close to factory spec (1.5 turn's out) the pilot circuit is pretty close to being correct
    But until you try it out on the road you won't know for sure, it may need some finer adjustment's once you ride it but it wont be too far off.
     
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    my67xr, Jun 21, 2017
    #209
  10. SwarleyAUS

    SwarleyAUS Well-Known Member

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    Yep, cool, was just wondering why you couldn't do it in first or second.

    So that method of testing I've read can be used to read the mixture across the whole rev range, if you chop the plug... need I do a chop to verify wot/main jet mixture or am I just looking for a coffee colour at the end of the insulator?
     
    SwarleyAUS, Jun 21, 2017
    #210
  11. my67xr

    my67xr Bike Enthusiast Staff Member Premium Member Contributing Member

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    It's pretty much for checking main jetting, and getting that coffee colour on the insulator
    The pilot circuit is adjusted more for feel, same with the needle clip

    The only way you'll get it perfect or close to it will be spending time with your bike on the dyno, making change's and running it again, but that can get costly in both jet's and the hourly dyno rate with labour
     
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    my67xr, Jun 22, 2017
    #211
  12. SwarleyAUS

    SwarleyAUS Well-Known Member

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    Right so the final issue I'm struggling to resolve is one that's come back to haunt me. She runs fine from a bottle still, but from the tank not so much. Symptom is that it struggles to rev, which I think is caused by insufficient fuel delivery. I've narrowed it down to being directly caused by the petcock, and I think it's due to poor vacuum under load. It seems the vacuum pressure is lesser when I rev the bike, versus at idle. This I judged from feeling the vacuum with my finger. Should I ditch the vacuum petcock altogether?
     
    SwarleyAUS, Jun 24, 2017
    #212
  13. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Have you checked this with the fuel cap on the tank open? The breather might be blocked which will cause the symptoms you describe.
     
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    Linkin, Jun 24, 2017
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  14. SwarleyAUS

    SwarleyAUS Well-Known Member

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    No, so try with the fuel cap off?
     
    SwarleyAUS, Jun 24, 2017
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  15. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Yes. If the tank breather is blocked, you get a vacuum in the fuel tank working against the vacuum of the carbs/motor, resulting in loss of fuel supply.
     
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    Linkin, Jun 24, 2017
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  16. SwarleyAUS

    SwarleyAUS Well-Known Member

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    Legend, she runs the same as off the bottle from the tank without the cap! So it's just a matter of disassembling the fuel cap and checking for sludge to remedy this?
     
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    SwarleyAUS, Jun 24, 2017
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  17. Linkin

    Linkin The Mechanic Premium Member Contributing Member Dirty Wheel Club

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    Yeah, the breather will either be in the cap itself, or there will be a passage from the cap area to the bottom of the tank which can get blocked up. Not sure which it is on the GSX250 as I've never owned one
     
    Linkin, Jun 24, 2017
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  18. SwarleyAUS

    SwarleyAUS Well-Known Member

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    This is my cap so I hope its in there cos I'm not aware of anything going out the bottom of the tank.

    1498285799130615896984.jpg

    I'm assuming this is the breather? Need to lube the ball or something?

    1498285901915-789701681.jpg
    IMG20170624163330.jpg
     
    SwarleyAUS, Jun 24, 2017
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  19. SwarleyAUS

    SwarleyAUS Well-Known Member

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    Gave that all a clean and she seems to be all good now! The larger ball bearing's chrome plating was everywhere so that must have been the cause. Cheers.

    She's still running quite hot though in my inexperienced opinion, gonna get some new plugs tomorrow so I can test jetting afresh.
     
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    SwarleyAUS, Jun 24, 2017
    #219
  20. SwarleyAUS

    SwarleyAUS Well-Known Member

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    Ok so brand new plugs and the result after a couple of power runs to 7k:

    19531830_10213677324706147_525793807_o.jpg

    What's the verdict? Right cylinder a bit rich at full load?

    Still a little bit of hesitation down low but seemingly better having oiled the pod filters properly =D
    https://www.facebook.com/video.php?v=10213677341546568
     
    Last edited: Jun 25, 2017
    SwarleyAUS, Jun 25, 2017
    #220
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