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Thread: 83 R100 Compression Test

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  1. #1
    Arctic Art
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    83 R100 Compression Test

    What is the best way? Seems like I have to warm up engine,take off front cover,disconnect bean can,pull or prop open carbs pull both plugs and put tester on cyl. That unplugging of the bean is a PIA. Is this it or is there a better/easier way. Thanks

  2. #2
    Administrator 20774's Avatar
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    I don't think you need to pull the bean can and the front cover. You do need to ensure that the engine won't fire. You can do that by dropping the float bowls...no gas, no fire. Also, put the plugs back into the high tension caps and secure the threads of each plug to the engine case...this allows the spark generated to find a path to ground, protecting the coils. Pulling the carbs is the best, but if you can prop the slide open on the carb, twist the throttle to open the butterfly, that will be OK for government work.
    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!

  3. #3
    Day Dreaming ... happy wanderer's Avatar
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    I may be going to check out an 82 RS next week. I was wondering about the compression test procedure. My RS has Bing 42mm CV carbs with the rubber diaphragms on top. Do these carbs have slides in them or just a long needle that comes down into the jet?

    I'd like to check compression with disturbing the carbs if possible. I read somewhere to just open the throttle wide open, ground the spark plug to the head and crank away. Cold or warm should not matter.

    Not so?
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  4. #4
    Administrator 20774's Avatar
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    Quote Originally Posted by Happy Wanderer View Post
    I may be going to check out an 82 RS next week. I was wondering about the compression test procedure. My RS has Bing 42mm CV carbs with the rubber diaphragms on top. Do these carbs have slides in them or just a long needle that comes down into the jet?

    I'd like to check compression with disturbing the carbs if possible. I read somewhere to just open the throttle wide open, ground the spark plug to the head and crank away. Cold or warm should not matter.

    Not so?
    CV carbs that you have have slides with a needle. But twisting the throttle only operates the downstream butterfly...it doesn't directly move the slide. So, you will need to remove the carbs, or as a bare minimum, remove the air tubes and prop open the slide and twist the throttle to open the butterfly. Actually, it would be easier to just loosen the clamps on the head-side of the carb and rotate the whole thing out of the way...you have to remove the air tubes no matter what. This won't disturb your carb synch.

    Warm engine would be better and give you a truer reading. Cold gives you a general idea and maybe what you want to do if you're looking at a potential bike.
    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!

  5. #5
    Day Dreaming ... happy wanderer's Avatar
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    Thanks Kurt.
    It figures that cheatin and the easy way is usually not the right way.
    MJM - BeeCeeBeemers Motorcycle Club Vancouver B.C.
    '81 R80G/S, '82 R100RS, '00 R1100RT

  6. #6
    Registered User lkchris's Avatar
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    It's super easy to simply pull the carbs off the manifolds and get them out of the way somehow. Without fuel dripping. No need to do anything to the cables. Without the carb attached to the manifold, things are by definition wide open throttle.

    Then just push the removed plugs back into the the wire connectors and lay them on top of the cylinders so they ground. The entire metal portion of the plug (the hex, the threads) is ground and it can easily contact a cylinder fin or two or the block. Just keep gasoline away from the spark.

    I recognize this is a little more difficult with the pre-1980 carb tubes, but still not that bad.

    You do know that the 1980-on carb tubes are removed by first sliding the rubber ring down on to the the plastic elbow. Then the assembly simply falls off.
    Kent Christensen
    21482
    '12 R1200RT, '02 R1100S, '84 R80G/S

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