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Thread: R75/7 Carb adjustment

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  1. #1
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    R75/7 Carb adjustment

    After cleaning both carbs and installation of o rings and diaphragms I have been trying to adjust them.
    The bike starts and runs reasonably well with a bit of a vibration. Once warmed up there is a bit of a backfire from the exhaust on deceleration. The plugs (dual plugged)on the right show it to be running a bit rich on that side.
    I do not have any type of vacuum balancing equipment. How do I get these things adjusted better?

    Info:
    1977 R75/7
    24000 orig miles
    Dual plugged
    Dyna 3 ignition
    recent valve adjustment

  2. #2
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    Apr 2011
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    Have you checked the timing on both cylinders? If I remember, the Dyna 3 uses two different pickups, one for each cylinder. So you can't just rely on timing the left and assuming the right is correct.
    You can get really close without even an el cheapo vacuum gauge.
    First run it one cylinder by grounding out the plugs on one side. Adjust the running carbs idle to something where it will idle by itself. Then do the same thing to the other side. Now when you start it on both cylnders, it will be running really fast. Just back the idle screws out the same amount on each side until you get a proper idle. Then you can fine tune the idle mix screws. Then with the engine off, stand on the right side of the bike, reach down until you can feel the left throttle arm where the cable attaches. Put your head where you can see the right throttle arm. Slowly move the throttle. You should see the right arm move the same time you can feel the left arm move.
    This synchronizes the carbs to their cylinder as well as making sure they open together. Worked for years on my 75/7.

  3. #3
    Administrator 20774's Avatar
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    Grounding plugs is a little difficult on a dual plugged machine. I believe Snowbum discusses ways of doing that.
    Kurt -- Forum Administrator ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  4. #4
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    I just went through this with my /6 and the problem turned out to be the float level was set too high.

  5. #5
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    Thanks guys
    I will re-read the snowbum thread, I have head so many horror stories about screwing up coils trying to ground out plugs.

    I will also read about -then try checking float levels

    As for the timing, that will have to wait, I did not know about checking both sides???

    I may need to find an airhead mechanic.

    Pete

  6. #6
    MOA #24991 Pauls1150's Avatar
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    That just sounds insulting...

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