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78E Carbs and a little extra info

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  • 78E Carbs and a little extra info

    Well, as some may know, I've had a couple of problems in the past 5 months with carbs, as if that's news to anyone with one of these beasts.

    After the bike had been sitting for 4 or 5 years, and the dealer trying to restore it to service, I picked this up for a song and a dance.

    Tore into the carbs, and rebuilt, cleaned, repaired, you've all been there. I even ended up with K&L (ugh) kits, along with everything else.

    And might I say thanks to TopCat, and all the others who have helped. But the best I could get was running on 3 cyc. #3 plug always wet with gas, exhaust pipe cold when running, 65 miles per tank, good spark, and would synch up. But the color tune continued to show lots spark, but no fire. No matter what was done.

    So I played with it when I could

    Finally ended up switching all the guts from #3 to #4, and the problem went to #4.

    Any way, got it purring perfect today. And here's the secret (at least for a 78E) I found out that the Mukuni Pilot jet wasn't seating all the way into the tube. After doing several side by side comparissons, with a 15x magnifying glass, I finally noticed a bright shiny ring, right on the very end of the tapered tip on three jets, but not my problem jet.
    I went and made a special tool for screwing it in, but that didn't work, I ran the jet through a 5mmx0.8mm die, that didn't do it.

    Finally grabbed my Ba$$s, greased up the tap, and put that 5.0mmx0.8mm tap into my carb pilot jet hole. Turned it 1 turn past where it stopped. Brought it out, cleaned it up, cleaned the carb, reassembled, and HOLY GOST POOP!! it worked.

    And further more, every one of the K&L Pilot Jets work also. But only in the carb I put the tap into. Using the color tune, I can put them right where I want them.

    Now as to why???? By measurement with a mic, the overall length of the 10 pilot jets I have vary by .009. I'm going to have to make a die to set them in to measure just lenght that is not threaded. I'll bet there's just enough deviation to cause some not to seat. I always thought they just screwed in until they ran out of thread, come to find out that tapered end sits against a stop.

    Perhaps we have part of an answer for some of the K&L's. But I definately have more respect for them FREAKIN Carbs.

    To all who gave me encouragement, when I wanted to blow this thig up, Thank You, Thank You, Thank you. I put 120 miles on my bike this evening, purred like a kitten, growled like a wet she cat, and I didn't have to stop for gas.


    Doo-Daa

    ______________

  • #2
    Congratulations on your discovery and thanks for relating it. The K&L horror database continues to grow. The issue I had with the K&L pilots was that they had NO holes in the sides, while the originals have FOUR holes.

    Without the holes there is no passage for the fuel to flow from the main jet passage to the pilot passage, resulting in wrong mixture at all throttle position except WOT.

    Randy

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    • #3
      Randy, I believe the holes in the sides of the pilot jets are air bleeds. But...you are right, wrong pilots are a nightmare!

      Originally posted by randy
      Congratulations on your discovery and thanks for relating it. The K&L horror database continues to grow. The issue I had with the K&L pilots was that they had NO holes in the sides, while the originals have FOUR holes.

      Without the holes there is no passage for the fuel to flow from the main jet passage to the pilot passage, resulting in wrong mixture at all throttle position except WOT.

      Randy
      Skids (Sid Hansen)

      Down to one 1978 E. Stock air box with K&N filter, 81H pipes and carbs, 8500 feet elevation.

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      • #4
        FYI:

        '78 and '79 carbs have different main jet tubes (can't remember the official name) for #2 & #3 verses #1 & #4. The tube I am refering to is the one the main jet threads into. I suspect this is how the early carbs compensate for #2 and #3 running a bit hotter. Swapping parts between #3 and #4 will mix these up. I doubt it will make a noticable difference.
        DZ
        Vyger, 'F'
        "The Special", 'SF'
        '08 FJR1300

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