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Thread: R75/5 Leaking Carburetor & ON/OFF Clutch Issues (Please Help)

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  1. #1
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    R75/5 Leaking Carburetor & ON/OFF Clutch Issues (Please Help)

    Hi all,


    So I seem to have two issues right now. Leaking carburetor (right side) and possibe clutch issue (freeplay is setup properly/etc)



    Issue #1: Leaking right carburetor.


    I've pulled the float bowl and checked the float needle. So far the needle follows the floats up and down. I tried flicking the floats up and down a number of times to make sure that there was no grit or anything stuck in the float needle. This seemed to work after having done it a good number of times. I rode around at around 20-30mph in a parking lot to test and what not. However the dripping carburetor started again after about 10-15 minutes.


    I checked the carburetor again and it looked like all was fine with the float needle. I then did a diagnostic test by holding the floats up while turning on the petcocks. No gasoline would flow when the floats were raised. When allowed to drop, gasoline would then flow from the carbs.

    Also I checked the float bowl to make sure it wasnt the problem. I had it filled with gasoline and there were no leaks once the filled bowl was removed from the carburetor.


    I dont know what else could be the culprit. The gaskets did look like they could possibly be old on the float bowl (they were darker colored) but I didnt see any gas from the tops of the bowls leaking out.




    Issue #2. Clutch ON/OFF action.

    I have set proper free-play on the clutch as per the BMW spec manual. The big problem I have with the clutch is that it is very ON/OFF in reaction. A friction zone is practically non-existant. There is a tiny bit of friction zone, but it makes it very difficult to have smooth clutch action. It definitely feels like a digital ON/OFF clutch.

    Is this normal? Is this due to clutch age/wear?


    My R75/5 has around 78,000 miles on it and it has not had any clutch servicing that I know of. None of my paperwork that I have for it mentions it being serviced.





    Hope you all can provide some help/suggestions.


    Cheers,

    Jonathan

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    Floats: The next thing I'd check is whether or not the float "floats". I'd remove the floats and put them in a container of gas and compare their buoyancy. Sometimes one will absorb gas and float lower in the fuel causing the needle valve to leak.

    Clutch: How much has the bike been ridden lately? I find the first ride or so of the season is a bit grabby but the more I ride the smoother things go. The clutch on my /6s and /7s never had a real wide friction zone but either they got better with use or I got better at feathering the clutch.

    After that you might need to look at such things as disc wear or contamination.

  3. #3
    #4869 DennisDarrow's Avatar
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    You did some very good and common sense diagnostics for the carb leak. Did you check for what the floats are set at? Meaning how much fuel is in the bowl before the floats rise enough to shut off the fuel flow by pressing the needle into it' seat. You dont mention doing this or checking the depth of fuel in the float bowl. Correct depth is 22mm Some folks say 27mm...........Let us know how that is.....God bless........Dennis

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    Registered User mneblett's Avatar
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    I second the "sinking float syndrome" guess -- the floats absorb chemicals from the fuel over time (years) and get too heavy to hold the needle valve closed all the time.

    Do you have any idea when/if the tranny input shaft splines have been lubricated? Sounds like the clutch hub is hanging up on dry and/or worn splines, and "jumping" from the disengaged position to an engaged position.
    Mark Neblett
    Fairfax, VA
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    Administrator 20774's Avatar
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    Not sure what BMW spec you have for the clutch adjustment, but this is the proper way to adjust it per BMW tech school:

    http://www.bmwmoa.org/forum/showpost...45&postcount=3
    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 DennisDarrow View Post
    You did some very good and common sense diagnostics for the carb leak. Did you check for what the floats are set at? Meaning how much fuel is in the bowl before the floats rise enough to shut off the fuel flow by pressing the needle into it' seat. You dont mention doing this or checking the depth of fuel in the float bowl. Correct depth is 22mm Some folks say 27mm...........Let us know how that is.....God bless........Dennis

    What is the best way to check the float settings?

    For checking the depth of fuel in the float bowl, would I simply turn the fuel petcock on and when the fuel begins to run from the carburetor overflow hole/tube, turn off the petcock and remove the bowl, then check the depth?




    Quote Originally Posted by mneblett View Post
    I second the "sinking float syndrome" guess -- the floats absorb chemicals from the fuel over time (years) and get too heavy to hold the needle valve closed all the time.

    Do you have any idea when/if the tranny input shaft splines have been lubricated? Sounds like the clutch hub is hanging up on dry and/or worn splines, and "jumping" from the disengaged position to an engaged position.

    I have no knowledge or paperwork on the input shaft splines having been lubricated. Is this a fairly costly thing to have done?


    Quote Originally Posted by 20774 View Post
    Not sure what BMW spec you have for the clutch adjustment, but this is the proper way to adjust it per BMW tech school:

    http://www.bmwmoa.org/forum/showpost...45&postcount=3

    Great! I didnt do it to this specifications, I just let about three to four threads on the hand lever be visible and then adjusted the clutch at the transmission side until the freeplay was around 5mm or so.

    I'll go through this procedure either later tonight or tomorrow morning to make sure I've got it correctly set.

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    Administrator 20774's Avatar
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    If you want to "ruin" an afternoon and your eyeballs, you might read Snowbum's article on the early /5 carbs...you didn't list a year of your bike:

    http://bmwmotorcycletech.info/earlybingR75CV.htm

    As for float height, you can do this by measuring the amount of fuel in the float bowl after you turn the petcock on for 10-15 seconds, then off, and finally remove the bowl. According to Snowbum, the height of the fuel measured in the center of the bowl should be ~24mm for the 32mm CV cabs. Snowbum has several articles on Bing carbs including synchonrization.

    For the splines, this might be something you can do yourself. There have been a few threads on this. But here is a pictorial of the general process:

    http://www.webbikeworld.com/t2/spline/

    I'll mention the Snowbum name again...he has an article on his website on doing this as well. It's not a colorful with pictures, but using the two websites, reading them in detail, finding the common elements and what's different, you should be able to do this yourself. Otherwise, it's going to be 4-6 hour job at the going shop rate...might begin to approach $500.

    When you have time between adjustments and reading, check out the link in my sig line...lots of good information there.
    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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