need carb. adjustment guidance

Discussion in 'General' started by bob66542, Jul 20, 2020.

  1. bob66542

    bob66542 New Member

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    went to the service manual and all it shows is a cutaway of the carb. went to the owners manual, all it says is set throttle stop screw to 1300 rpm, then turn air screw in and out to acheve highest rpm. how is the best way to determine 1300 rpm? there is no tach. Im sure there have been lots of inquiries on this subject, but I haven't been able to find them.
     
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  3. lukelaw1

    lukelaw1 Active Member

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  4. bob66542

    bob66542 New Member

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    so 1300 rpm is just a ballpark? a very fast idle?
     
  5. racerx

    racerx Administrator
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    1300rpm is a fairly slow idle for a single. Lawnmower engines typically idle at 1750rpm. And, yes, you can go be ear. The make-or-break number is clutch engagement rpm. Semi-automatic operates as a centrifugal clutch at low rpm. As long as it disengages at idle, you're fine. If rpm is high enough to cause centrifugal engagement, it's running clutchless from a dead stop and that's going to be a big problem. Best guesstimate, centrifugal engagement is somewhere around 2000rpm.

    Shift into first gear. If the engine idles and the bike doesn't move forward, idle rpm is acceptably low.
     
  6. bob66542

    bob66542 New Member

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    got it. thanks.
     
  7. bob66542

    bob66542 New Member

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    set the idle and mixture. mixture screw about 5/8 turn out. couldn't get it to speed up any to speak of turning it further out. it starts great, and runs fine at full throttle, but has a kind of off idle/ midrange stumble that is annoying. tried running it with the mixture screw out about 1/8 turn further out in steps up to about 1 1/8 turn out and it didn't seem any better, maybe slightly worse. what should I try next?
     
  8. bob66542

    bob66542 New Member

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    after setting when warm Tuesday, I took it out Wednesday , and cold, it stumbled more than it had previously, so I choked it some while riding to warm it up . when warm, with the choke off, it still had the off idle/ midrange stumble, but if I ran it with the choke just slightly on, it ran a LOT better- but then when I got home, it didn't want to sustain an idle without a little help. I am frustrated.
     
  9. racerx

    racerx Administrator
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    Sounds like you may have either an air leak, a partially-clogged fuel circuit, low fuel level inside the float bowl or some combination of these. Pull the throttle slide, the jet needle, then relocate the c-clip 2 grooves lower than it is, at present.



    You're over-relying on the pilot airbleed adjustment. That only has a noticeable affect up to about 1/8 throttle. If you need to increase idle speed, use the throttle stop/curb idle adjusting screw, located on the LH side, inline with the throttle slide centerline.
     
  10. bob66542

    bob66542 New Member

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    I will give that a try tomorrow. thanks.
     
  11. racerx

    racerx Administrator
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    Okay, here are a few pix that will hopefully clarify things a little. The emulsion tube holds the main jet. It also has a hex head...used to remove & reinstall. Unscrew it from the carb body, then run a wire through each of the tiny holes in the walls. This is a critical step in the rebuild process. Chemical cleaning, alone, will not get the job done and that's lead to more frustration than any other carburetion issue. The rest should be self-explanatory. That fine mesh fuel screen will eventually become clogged. Pump gas contains a lot of debris.
     

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  12. bob66542

    bob66542 New Member

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    thanks for the pic's. I've got work to do!
     
  13. racerx

    racerx Administrator
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    The fabled emulsion tube:
    DSC08329.JPG
     
  14. bob66542

    bob66542 New Member

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    Friday I moved the clip on the needle down(towards the end that goes into the carb body) 2 notches. it was in the middle groove, now in the lowest groove. It seemed to have a little more power, but still stumbles off idle/ midrange runs fine top end. Today I pulled the carb and disassembled it. ran very thin wire thru both jets and all the holes in the emulsion tube- 2 or 3 may have been at least partially blocked. all the jets, adjustment screws and emulsion tube and carb body are in carb. cleaner now. the float level is about 23 mm. will put it back together tomorrow. anything else I should do prior to reassy.?
     
  15. bob66542

    bob66542 New Member

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    Racerx- thanks so much for your guidance. after cleaning the carb using your recommendations, I put the clip on the needle back at the orig. setting and it now runs like a top! ran it about 5 mi. yesterday in short hops and adjusting, and then checked cold start, idles good, took it for a ride and it runs perfect and idles hot well also today, so I think its cured.
     
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