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Old 11-25-2012, 09:12 PM   #1
jbf OP
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Two Problems: Leaking Carb & Clutch ON/OFF Issue. (Freeplay is correctly adjusted)

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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Old 11-25-2012, 09:47 PM   #2
Big Bamboo
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Sounds to me like the floats need changing and the input splines need lubing. Original clutch? Any mention of these in those service records? Does the bike jump forward when shifted into first from a stop?

Big Bamboo screwed with this post 11-25-2012 at 09:59 PM
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Old 11-26-2012, 12:37 AM   #3
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The clutch is original (per my first post). When shifting into first the bike does jump forward but only when I let out the clutch. If the clutch lever is pulled in it doesnt lurch forward, but it does as i let the clutch out (super slowly as well).


I figured it would probably be the floats. Those I am pretty sure I can probably change on my own. Just need to get the parts.
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Old 11-26-2012, 01:05 AM   #4
disston
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What BB is suggesting is an input shaft lube for the sticky clutch. The transmission needs to come out to do this and you can take the clutch apart also to check it's condition and thickness. Also if the rear main oil seal is original you may opt for a new one of those. The input lube part of the job is applying some special grease to the input splines of the transmission. This is reported to alleviate shift/clutch problems by some people but is also reported to be a waste of time by others.

The dry type clutch in a BMW is more on/off than a wet clutch you may be comparing it to.

There are ways suggested to check the operation of the floats in the carbs. You can weight them. Float them in raw gas. And check the color. Nothing will tell you for sure you need or don't need floats. I replace mine when I think they are bad.

Float needles are often replaced if replacing the floats. But look at the tip with a glass to see it's condition.

The float needle seat can be replaced but it's not a really simple job. What you can try first, before replacing the seat, is polish it with some Brasso on the end of a Q-Tip and rotate the Q-Tip in the brass seat.
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Old 11-26-2012, 05:43 AM   #5
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Clutch Cable Adjustment - The Tom Cutter Method

You might want to make sure that you have adjusted the clutch cable free play correctly. The procedure below aims to ensure that the clutch actuation lever at the rear of the transmission has the optimum mechanical advantage. It makes a big difference. The method is often credited to Tom Cutter, but is really just a pragmatic interpretation of the BMW spec.

The first adjustment is made with the large threaded adjuster at the top, lever end of the cable. You need to measure the cable dimension at the LOWER end, and make the adjustment at the TOP end. The dimension should be EXACTLY 201 mm from the rear face of the transmission where the cable comes through, to the near edge of the cable barrel. You may need to turn the top adjuster out quite a ways to obtain that dimension. Squeeze the clutch lever and remeasure, as that will seat everything. The easy way to measure the 201 mm is to cut a piece of coat hanger to the exact length and use it as a gauge. Keep the tool around it is very useful.

The second adjustment is made at the rear of the transmission, using the adjuster screw and locknut on the clutch arm. Turn the adjuster bolt in until there is NO free play on the cable, determined by lightly pulling the lever with one finger and looking at the gap at the hand lever where the cable passes through. Once you have removed all free play, back out the adjuster just enough to give 2-4 mm freeplay at the hand lever. To hold the adjustment while securing the locknut, just pull and hold the clutch in with your left hand while snugging the locknut with your right hand.
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Old 11-26-2012, 05:57 AM   #6
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What condition is your clutch cable in? You could have some wear and binding, causing uneven release as you let out the clutch.
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Old 11-26-2012, 06:09 AM   #7
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bush repairs

I had this same problem with the carbs.. a wet foot while riding isnt fun at all. sitting on the side of the road I tweaked and tweaked on the carb adjustments but after a few minutes it would always start dripping again.. not wanting to drip fuel all the way home I pulled out my leatherman and bent the little tiny tab that pushes the pin on the float bracket up just a tiny bit higher.. problem solved..and I havent had a gassy foot since.
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Old 11-26-2012, 06:53 AM   #8
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Quote:
Originally Posted by raysthebmw View Post
what condition is your clutch cable in? You could have some wear and binding, causing uneven release as you let out the clutch.
+1
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Old 11-26-2012, 08:01 AM   #9
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I'm betting either a new clutch cable or a spline lube (or maybe both) will have your clutch working correctly. As for the carb it could just be a matter of bending the tang up just a bit more to shut off flow a bit earlier. I believe the spec is that flow should stop with the floats basically parallel to the mating surface on the bottom of the carb. As the floats age though, they soak up gas and gradually float lower and lower in the gas permitting a higher level of gas in the bowl. Short of replacing the float, you can bend the tang up a bit to bring the level back down.
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Old 11-26-2012, 11:27 AM   #10
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Input shaft end float.

Too much end float in the gearbox input shaft will also give you that on/off clutch action.
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Old 11-26-2012, 01:34 PM   #11
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Quote:
Originally Posted by Mogas View Post
Too much end float in the gearbox input shaft will also give you that on/off clutch action.
Can you elaborate more? I have no idea what this means really.
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Old 11-26-2012, 02:14 PM   #12
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Quote:
Originally Posted by jbf View Post
Can you elaborate more? I have no idea what this means really.
What jbf is taking about is part of transmission rebuilding. If you do everything else and it's still not right the trans can be taken apart to check the end play of the three shafts. Probably need some other parts by that time too. And it'll be so far in the future from now you'll need a new clutch and some other stuff.
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Old 11-26-2012, 03:20 PM   #13
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Quote:
Originally Posted by disston View Post
What jIf you do everything else and it's still not right the trans can be taken apart to check the end play of the three shafts.
No need to disassemble the trans to check end play on the input shaft. Just pull the trans and put a dial gauge on it and push it in and pull it out. Heat the whole thing up to operating temp and check it again for variety. I don't think that's the problem here though.
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Old 11-26-2012, 10:23 PM   #14
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Yeah I hope I can get by at least a year or two before I have to rebuild the transmission. I know its a high mileage bike and all but hopefully its something just like the splines/etc. I'm going to re-do my clutch adjustment tomorrow morning and also try to fix the float issue as well. I'll ride it around for a good few miles tomorrow and report back.


Cheers all,

Jonathan
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Old 11-27-2012, 05:04 AM   #15
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Float height:
For the 32 mm carburetors, use 24 mm fuel height.
For the 40 mm carburetors, use 28 mm fuel height.

Be sure to measure in from the center of the recess in the float bowl. I have a small file I've notched that I use for measuring tool.
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