CV Carb Idle Trimming Problems

Discussion in 'Engine, Fuel and Exhaust' started by ccryder, Mar 2, 2013.

  1. ccryder

    ccryder Member

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    Hi Everyone, Working on my '96 Spcn Heritage, 80", Ultima ignition, Ev-27 cam, 2 into 2 pipes,.050 shaved heads, modified Keihin Cv carb.
    I bought this Cv carb a couple of years ago. It already had the Cv performance kit installed in it. It runs real good, except for being able to "Trim" the idle mixture correctly. Today I found out that the Pilot jet is a #48. I can turn the idle mixture in slowly all the way in to it's seat, and no change in idle quality or speed! So..I went to a #46. Now...I have to turn mixture out about 5 turns to get any quality idle. By now it's ready to fall out of the carb!
    So...Back in with the #48 I guess. Since #47's are not available.
    One thing I'm wondering about...is a little "o" ring on the idle mixture screw. If it was missing, what would the negative effects be?
    Any thoughts? Thanks! Doug
     
  2. NEWHD74FAN

    NEWHD74FAN Experienced Member Retired Moderators

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    Missing the O-ring means air can leak around the threads, negating the adjustment. Probably why screwing all the way out with #46 works, and why #48 does not. Also check that the mixture screw surface is not grooved, if so, the seat cannot be much better, so you might have to replace at least the screw too! :)
     
  3. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

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    What he said. You need that o-ring, it acts as the packing for the needle.
     
  4. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

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    Getting a carb right can be a wee bit complex especially if a performance kit has been fitted
    First thing to do is replace the missing o ring as it prevents air from being drawn past the threads of the screw
    As fuel is fed by both main and slow jets during idle if the 46 is too small and the 48 is too large try adding a wee bit more fuel from the main jet by fitting the 46 slow jet and adding washers under the seat of the main jet needle this will raise the needle slightly and due to the taper on the needle will allow more fuel through at all throttle openings
    This might take a wee bit of trial and error to get it just right
    If however there are already washers under the needle seat try the 48 slow jet and remove a washer or 2

    Brian
     
  5. ccryder

    ccryder Member

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    Good Morning, Thanks for all your replies! Yes, I will check for the little O ring on the EZ-just mixture screw first. Haven't yet, but was reading about the existence of it on one of these forums.

    After reading, it just seems like running a #48 pilot would be too fat for a mild build like mine. Plus the fact that it is un-trimmable. Something's wrong!
    Now,should this evasive O ring come out with the mixture screw, or do I need to turn the carb upside down & fish it out?
    As for the tapered jet needle...isn't that for coming off idle to mid-range control? Does that also influence idle quality?
    When I tried the #46 pilot and got it to run with it...the exhaust tone changed to a cleaner, barkier tone! Think I was running a lil rich with the #48.
    These are Great Carbs! I've had Linkerts, Zeniths, S&S, SU's on various Pans, Shovels,etc over the years. And, this carb...Great roll-on, no spitting, just the little idle/mixture issue! Thanks again! Doug

    P.S. Plugs look a whiteish tan!
     
  6. Jack Klarich

    Jack Klarich Expert Member

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    White to tan looks good on the plugs IMO CV Performance Parts Have a look here about the o rings and spring on that screw
     
  7. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

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    All the jets are producing fuel all the time so raising the needle a wee bit should add a wee bit more fuel at all throttle positions
    it may also be worth checking the operation of the enricher to ensure it is opening and closing fully

    Brian
     
  8. 84FXRS

    84FXRS Member

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    put down a white towel to work over before you, turn over the carb to retrieve the
    o ring. They have a habit of getting lost easily. adjustment or shimmming the needle should not affect the idle.
    Go to the site as suggested by Jack, you should find all the info you need there.
     
  9. Slo-Ryd

    Slo-Ryd Junior Member Contributor

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    Fin hits on another critical area to watch. The end of the enrichment valve has a rubber ring impregnated into it to seat and prevent any fuel from seeping past when the choke is fully closed. Also check for the spring at the 90* elbow that secures the enrichment valve onto the carb. The spring goes between the valve and the plastic fitting on the elbow. I've seen an example on a bike I worked on for a friend that was missing the spring and not allowing the choke to fully seat leading to a rich condition and idle mixture adjustment problems.
     
  10. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

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