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Thread: R75/6 Carb Issues?

  1. #1
    Registered User kentuvman's Avatar
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    R75/6 Carb Issues?

    A friend is restoring an R75/6 - he sent the carbs to Bing for overhaul.

    The bike starts and idles but under a load, starts to die. Does this sound like a carb issue? I suggested he check the timing and he says he set the valves properly.

    I'm thinking carb's - he has new fuel petcocks and tank is clean.
    Ken Tuvman
    Excelsior, MN
    K75s, R65LS, R60/5

  2. #2
    Superkraut typ181r90's Avatar
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    Maybe float height set incorrectly?
    // 1975 BMW R90/6 (cafe'd) // 1957 BMW R60 (in pieces) // 1967 Aermacchi/H-D Sprint 250 SS (custom special) // 1973 VW Type 181 Custom SOLD )

    http://symphonyofshrapnel.blogspot.com

  3. #3
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    Does he know the difference between "timing" and "valve setting"?

    Timing has to do with spark timing, which, if off, can affect its running.

    Why doesn't he run some checks on carbs before sending them out. Bing wants you to pay with your firstborn!

    I would check things like diaphragms, all jet openings, float levels, all the settings before I would go drastic.

  4. #4
    Registered User kentuvman's Avatar
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    Quote Originally Posted by jimmylee View Post
    Does he know the difference between "timing" and "valve setting"?

    Timing has to do with spark timing, which, if off, can affect its running.

    Why doesn't he run some checks on carbs before sending them out. Bing wants you to pay with your firstborn!

    I would check things like diaphragms, all jet openings, float levels, all the settings before I would go drastic.
    He already spent the big bucks having Bing overhaul the carbs - I suggested he call Bing to find out if they'd pre-set the air & idle screws - I've got a carb synch tool but he does not - haven't been to his place yet - just trying to do some "pre-op" work for him.
    Ken Tuvman
    Excelsior, MN
    K75s, R65LS, R60/5

  5. #5
    Registered User lkchris's Avatar
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    After proper setting of valves is verified, check compression.
    Kent Christensen
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    '12 R1200RT, '02 R1100S, '84 R80G/S

  6. #6
    Registered User kentuvman's Avatar
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    Quote Originally Posted by lkchris View Post
    After proper setting of valves is verified, check compression.

    He did replace cylinders, pistons, rings & valve job - will suggest he check that - hope he did it right! - wonder if he positioned his rings correctly?
    Ken Tuvman
    Excelsior, MN
    K75s, R65LS, R60/5

  7. #7
    #4869 DennisDarrow's Avatar
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    By "under load it almost dies", what does it actually do. Usually if one is riding at let's say 4K RPM and then go WFO on the throttle it should just really GO.........if, when you roll on the throttle and the engine goes kinda flat and have no power at all and then catches up with itself and begin to pull; but no real POWER........or what?????................For me that is a torn diaghram(pardon spelling). I understand that he already sent it out to BING for a rebuild; but they are just human and there could really be problems with that.........God bless......Dennis

  8. #8
    Registered User dmftoy1's Avatar
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    I suspect the bings are fine, but I'd start check the flow rate into a cup with the bottom cover removed to verify flow rate. It's on snobum's site and is something like 220 or 320 ml a minute. If you don't have that then backtrack. Does opening the gas cap give proper flow? If so look for venting problem. If flow rate is good I'd assume carbs are probably on and check timing, advance, etc. etc.

    I'd also check that cables are adjusted properly, enrichenenrs go off correctly, etc.

  9. #9
    Registered User kentuvman's Avatar
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    Update

    Well, the reason why was the timing was off -- brought the Northwood Airheads points tool and first set the points, then we timed it. Friend had Bing overhaul the carbs, which are perfect. We adjusted the clutch and he broke the black wire that goes to the points & up right side of timing chest (or left side if you're in front of bike) - the wire wasn't tucked properly and got caught in advance mechanism.

    He's happy - his bike is running pretty good and he can now move on to other things like brakes, etc.

    R75/6 - a nice one.
    Ken Tuvman
    Excelsior, MN
    K75s, R65LS, R60/5

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