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Project My project MC22

Discussion in 'Your 250cc Projects' started by Krompot, May 21, 2020.

  1. Krompot

    Krompot Active Member Premium Member

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    Not weak spark, turned the lights off and it's a fat blue spark.

    I think this image belongs in this thread
    [​IMG]
     
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  2. Krompot

    Krompot Active Member Premium Member

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    She works!

    Tomorrow I ride it again for the first time in 1.5 years.
     
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  3. kiffsta

    kiffsta Administrator Staff Member Contributing Member Dirty Wheel Club

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    congrats on getting it running , now ride it like you stole it
     
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  4. Krompot

    Krompot Active Member Premium Member

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    Let's hope I don't go deaf while i'm at it...
    I've bought a baffle from china. It's wayyyy too loud.
     
  5. Jo Verhelst

    Jo Verhelst Forty2 Premium Member Contributing Member

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    tooloud.jpg
     
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  6. Krompot

    Krompot Active Member Premium Member

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    uh oh...

    What I initially thought was bad fuel is indeed not.

    There is a severe flat spot at idle-2500rpm. It revs quick, drops back down to idle quick. Thought I had it tuned properly.
    It's alright on flat ground, but hill starts are impossible. It will start going, then get stuck at 2000 (Opening throttle changes nothing) until I pull the clutch to rev it, then slowly slip it till it's beyond the flat spot. It *seems* to behave well at other rpm (haven't gone above ~12k)

    Is this a pilot screw setting issue? The carb boots are new and I don't think there are leaks. New pilot screws, seals, washers and springs.
    The screws are at 2+1/8th turns each (stock = 1+3/4), I used Litetek's carb tuning by ear guide (plus throttle response). The bike needs choke to start, and dies quickly with choke on once it's warmed up. Is this set up properly?
    These are VP20A carbs.

    Any thoughts appreciated.
     
  7. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    It might be that your 'ear' is not as good as you might hope. Set the mixture screws at 1-1/4 and see what happens. Then set it at 1-1/2, keep going until you find the sweet spot. All this has to be done with a warm engine of course.

    "The bike needs choke to start, and dies quickly with choke on once it's warmed up." That is how it should be.
     
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  8. DannoXYZ

    DannoXYZ Well-Known Member

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    Also make sure that petrol passage from pilot-screw to carb-venturi and its bleed hole is clear.

    Scrub passage with small brushes using fuel-system cleaner with high dose of PEA. Gently poke through bleed hole with soft copper wire from venturi end.
     
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  9. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    What Danno said, the most likely problem in carbs is the smallest one - the pilot circuit.
     
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  10. Krompot

    Krompot Active Member Premium Member

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    Hi,

    Got the bike running nicely now. Here is an audio clip:
    On decel, there isn't popping/backfiring, but a bit of a gurgle. I like the sound of it, but does this suggest something improperly tuned? Around 65 seconds is a good example.

    Thanks for all the help guys!
     
  11. jmw76

    jmw76 Well-Known Member Premium Member

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    It doesn't sound too bad.
    A re you still running your "loud" exhaust? If so. It might be contributing to a bit of lean out when you back the throttle off. Try adjusting the idle screws initially to make it a bit richer when the throttle is closed.
    Unfortunately, as soon as you change anything from standard you will need to tweak the tuning a bit.
    Good luck, but making good progress.
     
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  12. Krompot

    Krompot Active Member Premium Member

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    Idle? Beautiful
    Throttle response? Quick
    Wide open? Awesome
    1/5 to 1/4 throttle? Nah

    Seriously... I can't figure this out. I have tried 1.5, 1.75 and 2 turns out on the pilot screws. All this changes, or what I can perceive as change, is the idle speed/throttle response and if it hangs/dies after revving.

    10 steps forward 9 steps back.

    At 1/5 to 1/4 throttle the bike behaves exactly how it does when it's running out of fuel. I'm not sure if it's all 4 cylinders or just two that do it. At the moment I have to slip the clutch enough to keep the revs up and use lots of throttle to get past the dead-spot.
    The video I posted was 1.75 +1/8 turns out.
    Can I fix this myself? Should I take it to a carb shop? Budget's tight... which circuit is responsible for delivering fuel at this throttle opening?

    Jet info: 105 102 102 105 mains, 35 slow? jets. Currently at 1.75 turns on the pilot screws. I believe this is stock. 150psi compression on all cylinders.

    Also, anyone know why spark plug insulators crack overnight? Always #1 or #2 plugs. Happened 3 or 4 times now. Replace it with a working plug and it runs fine. I'm not over-tightening them. Just snug.

    20210707_153815.jpg Washed the bike today.
     
    Last edited: Jul 7, 2021
  13. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Now I know it might seem like a stupid question but have you ever ridden another 250 4? They have no power at all down low.
     
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  14. Krompot

    Krompot Active Member Premium Member

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    Yes, I have owned two bandit 250s and have ridden a hornet 250, as well as having this bike as my daily for just over a year (till I wrecked the engine)

    I'm not kidding when I say it's as if it's running out of fuel. Like when you need to swap over to reserve.

    There's more power at 1/8th open than there is at 1/4. I can feel the low spot if I slowly go from closed throttle to WOT
     
  15. GreyImport

    GreyImport Administrator Staff Member The Chief Contributing Member

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    Is the fuel tank breather working ? .... open the cap a little and see if it does the same .... it will create a vacuum if its blocked

    Does it have an inline filter ? ... is it new ? ... installed in the correct direction?
     
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  16. Krompot

    Krompot Active Member Premium Member

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    Already tried the tank cap thing. No fuel filter...
    It's not an issue of fuel flow into the carbs. I've filled them without the tank on (using a funnel) and it does the same going up the driveway.
     
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  17. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Are the carbs balanced?
     
  18. Krompot

    Krompot Active Member Premium Member

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    Yep. Bench sync'd then used cheap vacuum gauge setup (each gauge was calibrated using #1 cylinder, then attached to their respective cylinders) to fine tune.

    Got them apart now... giving them a soak in threebond... again. Double checked, all the jets are stock size. Nothing was blocked. Slides move as they should. Needles in good condition. Threebond came out the pilot circuit air intake when sprayed down the slow jet hole, when the air inlet is covered and sprayed down the slow jet hole it comes out the pilot screw hole, and when sprayed down the pilot screw hole it comes out the venturi side.

    Will post update when they're back on bike.
     
  19. jmw76

    jmw76 Well-Known Member Premium Member

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    What is the condition of the intake rubbers?
    They do not have to leak much to really stuff things up on these little motors.
     
  20. Krompot

    Krompot Active Member Premium Member

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    They're new

    Have a look at the video I posted earlier. The carbs behave very nicely at idle.
     

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