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Thread: Carb sync

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    Carb sync

    I have set my carbs as Clymers suggested. Then I adjusted my valves to their spec. Then I connected carb synchronizer. I use the kind with mercury in tubes and the idea is to equalize the height of the mercury in two tubes. Do I do this at idle or some other RPM?
    Campbell Tellman II
    1993 R100RT

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    Administrator 20774's Avatar
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    Both. At idle, you will be setting the idle mixture and the idle speed. You will need to do one, then the other, and go back to the first as they interact with each other. Then you need to set the throttle cable tension...do this by running the RPM up to 1500-2000 and adjusting the tension in the cables. Generally, you want to take the carb which has the higher speed (vacuum) and lower it by decreasing the tension in the cable. The reason is that if you increase the tension in the slower carb, you run the risk of reducing the slack that you initially started with. That messes up the idle settings.
    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!

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    #4869 DennisDarrow's Avatar
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    For me, and you will get varied responses to this subject with each having their own merits, I use the values achieved with mercury sticks or even the el cheapo $4 guage to check out idle air screw adjustment, idle speed, and then up where I cruise or get full advance on the timing curve. There are reasons for using them at each place; but I find that they are a great double check for the idle speed and stuff; but what really matters is getting the engine running smoooooooth at the RPM where I ride.
    NO I do not spend a lot of time making the adjustment at 3K RPM; but we are only talking about perhaps tightening or loosening one of the cables by 1/8 of a turn at the most to get it right.

    ALWAYS..........take a ride to warm up the engine before you make these adjustments.......NOT around the block but 10 to 20 miles.........

    Use the largest floor fan you can get in front of the engine while making the adjustments. The whole thing should take more than perhaps 5 minutes; but that short bit of time can really put a lot of heat stress on one's engine.........

    God bless.........Dennis

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    Bing Instructions . . .

    I have a set of instructions from Bing. It will allow me to do a proper synchronization. Thanks for your help!
    Campbell Tellman II
    1993 R100RT

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    Mercury

    Need any mercury? I think I have some flowing around my shop, it's probably trying to find a lower point.......get that thing going, let's ride somewhere!

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    A Source for Mercury

    After I spilled the synchronizer and lost most of the mercury I went to my Dentist and he said "I have some and don't use it anymore." Ergo he gave me a big container to refill the synchronizer!
    Campbell Tellman II
    '93 R100RT

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    Quote Originally Posted by CTellman View Post
    After I spilled the synchronizer and lost most of the mercury I went to my Dentist and he said "I have some and don't use it anymore." Ergo he gave me a big container to refill the synchronizer!
    Campbell Tellman II
    '93 R100RT
    Did you make out a report to the EPA? There is probably some fish swimming around in the Atlantic with its eyes glowing!

    BTW I am JUST KIDDING!!!

  8. #8
    Day Dreaming ... happy wanderer's Avatar
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    Be careful with that stuff. It was banned for good reason.

    Here's just one small excerpt from the Agency for Toxic Substances and Disease Registry Tox FAQs

    How can mercury affect my health?

    The nervous system is very sensitive to all forms of mercury.
    Methylmercury and metallic mercury vapors are more
    harmful than other forms, because more mercury in these forms
    reaches the brain. Exposure to high levels of metallic,
    inor*ganic, or organic mercury can permanently damage the brain,
    kidneys, and developing fetus. Effects on brain functioning
    may result in irritability, shyness, tremors, changes in vision or
    hearing, and memory problems.

    Short-term exposure to high levels of metallic mercury
    vapors may cause effects including lung damage, nausea,
    vomiting, diarrhea, increases in blood pressure or heart rate,
    skin rashes, and eye irritation.



    Hard to believe we used to play with this stuff when we were kids!
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

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    Quote Originally Posted by happy wanderer View Post

    Hard to believe we used to play with this stuff when we were kids!
    I used to play with it too when I was in the 3rd-6th grades.

    Perhaps that is what is wrong with me!

    I don't think it was banned completely was it?

    I know that they took it out of switches (furnace thermostats, for example), and replaced with electronic switching.

  10. #10
    Registered User bluegrasspicker's Avatar
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    Tom Barrie
    http://bluegrasspicker.blogspot.com/
    2012 K1600GTL
    2002 R1150RT (sold)

  11. #11
    Administrator 20774's Avatar
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    Quote Originally Posted by sirsethro View Post
    yank off one of the spark plugs. Bike should run just fine on one cylinder.
    This was a method for the older bikes with magnetos as they had a safety gap to allow the spark to find ground. Generally not recommended on bikes with coils, and certainly not a good thing for a bike with electronic ignition. But you've been doing it for years...guess you've dodged that bullet. Still, not a good thing to do especially when there are relatively easy ways that don't stress the ignition system. My 0.02.
    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!

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    Quote Originally Posted by sirsethro View Post
    You guys seriously have mercury just floating around the shop? mind=blown

    I just tune my carbs by ear. .
    I like the old school method, too. However I have heard that there is some truth to what Kurt says (and it is logical) that by just pulling off the plug wires while the bike is running could hurt the ignition system, particularly the coils or with electronic, the electronics.

    What I do, is to take along a screwdriver and a 10mm wrench, and do some rough adjusting of idle MIXTURES after riding about 10 miles (find middle of too lean & too rich on each carb). This takes me about 1 or 2 minutes. Then I adjust the idle SPEEDS with the adj. stop screws, making sure each side hits the same (feel exhaust pressure with your hands).

    So as not to overheat anything, I go riding some more, and find another quiet parking lot.

    Do idle MIXTURE & Idle Speed again. This time I also do the cable balance at around 2,000 RPMs. Lowering the Higher running side until they both sound the same, AND that the same amount of pressure is expelled out of the exhaust pipes (by placing a hand just behind each muffler and feeling the pressure and judging which is greater).


    I then go out and ride some more.

    I wait a week, do some riding and do the process one more time to let things "settle." I find that If I keep doing something every time something seems amiss, (like balance or slight vibration), I am constantly changing things and can never get a handle on any one thing!

    I have tried what Bing recommends - to get the idle mixtures as lean as possible without engine dying. However, I didn't learn this way, and because I am afraid to get the thing too lean and do some damage, I generally back out screws to the middle spot between too lean, and too rich.

    However I never just pull the plug wire. If I want to do isolate a side, I use a ground to cylinder to the other side's spark, so it can still "find" a release to ground. Still isolates cylinder, but doesn't do any damage to system.

  13. #13
    Benchwrenching PGlaves's Avatar
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    Quote Originally Posted by sirsethro View Post
    Well, in the end experience trumps luck. It's probably only a matter of time until I break something. I'm glad I posted my method, learned something new today.

    I do have those plug grounding tools from Northwoods Airheads, I believe they're called "BMW Airhead Carb. Sync. Adapters"

    They were a bit fussy for me to mess with on the road, but if there's the potential to damage the bike then they seem like a good way to still sync the carbs by ear safely by grounding out the plugs one at a time.
    On-the-road is the worst place to fire high voltage to an ungrounded plug wire. If the ignition trigger fails you are stuck until the tow truck arrives. In the shop you can at least roll it to the corner and wait for the part.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

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    Benchwrenching PGlaves's Avatar
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    Quote Originally Posted by CTellman View Post
    I have set my carbs as Clymers suggested. Then I adjusted my valves to their spec. Then I connected carb synchronizer. I use the kind with mercury in tubes and the idea is to equalize the height of the mercury in two tubes. Do I do this at idle or some other RPM?
    Campbell Tellman II
    1993 R100RT
    Long answer. Caveat: folks do it different ways. Here is how I do it and why.

    Engine warmed up, box fan blowing from the front.

    1. Adjust the cables so there is slight slack at each adjusting ferrule. I like about 1mm slack.

    2. Adjust the idle speed screws to equalize the vacuum on the two sides.

    3. Loosen the locknuts on the cable adjusters. Turn the throttle until it is just off idle and on the cables. Adjust the cable adjusters until the vacuum is equal and you still have slight slack in both cables when returned to idle.

    Now the why. You are attempting to set the throttle plate angles the same. You are using vacuum as a surrogate for airflow which is itself a surrogate for throttle plate angle. At the lowest RPM while on the cables, the cross section for air is a very small crescent, and any slight angular difference in the throttle plates will be a significant percentage of air flow, and vacuum. At larger throttle openings slight angle differences don't result in as significant vacuum changes. You get maximum sensitivity and accuracy at the smallest throttle openings.

    I also know that some folks have engines that seem out of synchronization at 4,000 RPM if synchronized the way I do it. This is not because of throttle plate angle however. It is because of other factors that interfere with air flow. Deposits on valve backs and stems, deposits in the intake tract, carbon in the cylinders, and valve adjustment are some of these factors.

    So I set my carbs to synchronize throttle plate angle as closely as possible at low RPM. Then, If synchronization drifts significantly off at higher RPM I look for and address the root cause which is disturbing air flow.

    Synchronization at road speed RPM is a good get-me-home strategy for a poorly running engine but that is the only time I would personally do it.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://www.bigbend.net/users/glaves

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