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

  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
    #32806

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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://forums.bmwmoa.org/showpost.ph...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://forums.bmwmoa.org/showpost.ph...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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    #4869 DennisDarrow's Avatar
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    YOU will be fine with your clutch adjusted the way you did it.......Kurt, for me, perhaps a bit tied to the "book" but it works and LOTS of folks go by that method. For MANY MANY years BMW recommended doing just what you did. Perhaps NO threads up at the hand lever and perhaps 2 to 3 mm of gap there with the lever on the back of the trans with 5mm of play.............

    To measure the fuel in the float bowl, turn off the petcocks, slip the bale back that holds the bowl on, take it off, measure immediately down in the center inside that little ring on the bottom of the bowl........Perhaps throw that out and measure again by putting the bowl in place and holding it with your hand, turning on the petcock a few seconds, turn it off, and then remove the bowl and measure again...........Adjust the floats by bending the little tab on the floats that rubs against the needle........JUST barely move it with a small screwdriver one way or the other....JUST BARELY....a little goes a long way............

    So what results did you have.........??????

    Since you got this thing how many miles have you actually put on it???......Warming it up in the parking lot is not a ride..........Get it out and put at least 20 miles on it........Do this over a few days and lets see how the clutch works......If it aint broke, dont fix it and before you go tearing into it....find out if it is really broken.........God bless........Dennis

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    Dennis -

    I used to adjust my clutch the way jbf did...more or less by feel but using the 4-5mm value of free play and having the hand lever "feel" more or less right.

    Then I bought a new clutch cable and decided to use Cutter's method...what a difference! Like butta!! Not sure why, but it must have been the proper position to get the most mechanical advantage from the lever at the back of the tranny.

    Works for me!
    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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    Clutch problem does not sound like cable adjust issue

    Suspect dry or damaged transmission mainshaft splines
    or
    transmission mainshaft moving in and out of case (need shim adjust)
    or
    bent clutch pushrod at the clutch end tip causing a groove to be cut into the pushrod which
    causes action you describe when clutch is actuated (pushrod can be bent when bolting the
    transmission to the engine if not centered - it will then get a wear groove near the clutch end)

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    Quote Originally Posted by 44006 View Post
    Clutch problem does not sound like cable adjust issue

    Suspect dry or damaged transmission mainshaft splines
    or
    transmission mainshaft moving in and out of case (need shim adjust)
    or
    bent clutch pushrod at the clutch end tip causing a groove to be cut into the pushrod which
    causes action you describe when clutch is actuated (pushrod can be bent when bolting the
    transmission to the engine if not centered - it will then get a wear groove near the clutch end)

    So what kind of financial damages could these scenarios be?


    Oh and it's a 1971 r75/5 with around 78,000 miles on it.

    Carbs are /11 (for the last set of numbers listed on them)

  12. #12
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    Probably trouble fix will be mostly labor
    Cost depends on whether you are going to do the labor or a shop

    I based what I have said previously on my understanding that you have the clutch adjusted in such a way that there is at least slight freeplay in the lever on the back of the trans when hands off controls and that when you pull the handlebar lever the cable moves the transmission lever such that the pushrod which actuates the clutch is actually pushed forward and you feel some resistance of the spring pressure and that at full clutch lever pull the clutch is actuated such that the motor runs in gear but does not drive the bike.

    As you release the clutch hand lever slowly you find no significant friction zone and take off with a jerk.

    And you are satisfied that the cable runs smoothly through its sheath and is not jamming up beause of being stranded.

    If the above description is true then I suspect one of the three alternatives in previous post or maybe some sticky stuff on the friction disk. No amount of messing with the cable adjust will get you any fix.

    In any event you need to first remove the transmission from the bike - it is time for at least a spline inspection/cleaning/lube and throwout bearing clean and lube and inspection cleaning and measurement of the clutch friction plate thickness. Also you probably should do this by leaving the engine mounts alone and letting the swing arm go back after removing the pivot pins. It is time to clean and lube those swing arm bearings so use this method rather than moving the engine forward as some do.

    If you are not the type to do this labor yourself then you need a very good airhead buddy to deal with - a professional shop will kill you on the labor.

    There is no difficult labor or skilled tech type stuff or special tools - just a bolt and unbolt the necessary pieces and remember how to put them back.

    Once you have the trans out and can clean up the splines you will know if they are damaged or just rusty and you can try to move the shaft in/out to detect movement from bad shim job. You can inspect the pushrod to see if it is smooth cylinder all the way forward to the beginning of the +-45 deg tapered tip that engages the clutch.

    Then tell us what you find.

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    Thanks for all the information everyone. Really helpful. I'll be attempting the carburetor tests and setting float level tomorrow morning.


    Out of curiosity, does anyone know the place I can get the best prices on a rebuilt kit for my 32mm bing carburetors? Also, what works best for removing the float pins? I'll need to source the tool for that as well.



    Cheers,

    Jonathan

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    Administrator 20774's Avatar
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    I've seen that getting Bing parts at Bing is not always the cheapest...weird. But dealers usually can get good prices on parts. You could look at BMW Hucky and Bob's BMW as well. MaxBMW gets high praise here...Rusty behind the counter knows Airheads.

    The knurled pin just needs to be drifted out using a small nail. You drift it out starting on the opposite side of the knurled part...the idea is you don't want to drag that knurled section through both bosses on the carb. Be careful...don't apply too much force...light taps should be all that is necessary to get the pin started out.
    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!

  15. #15
    Jack Ethridge
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    Ref overflowing carb. To check the fuel depth in the float turn the gas on then turn it off when the bowel has filled. Disconect the fuel line at the CARB, otherwise you will get the gas in the line in the float bowel. Lifting the float with your hand is not a good test as you put more pressure on it than the gas. Done that and gas shut off yet overflowed when bowel reinstalled. Fuel depth 1/2 inch from top of the bowel is a good test. Now, clean the needle seat with a Q tip and Brasso. Install NAPA in line filters. Checking the floats as said is good to do. I piesce of wire holding both floats up should give you an indication that the floats float the same. Bending the tabs to adjust the floats should not be needed as there is nothing that changed to floats unless they don't float right.

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