The New And Improved Unofficial R65 Forum V2
Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: AlfromNH on November 27, 2013, 03:50:53 PM
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I bought the carb kit that includes the diaphragms. I read snowbum's article but am still not sure how to get the old diaphragm off the slide, or the new one on. I tried simply pulling it off and only succeeded on tearing the rubber.
(https://bmwr65.org/smf/proxy.php?request=http%3A%2F%2Fi1350.photobucket.com%2Falbums%2Fp763%2Facarey3%2FIMG_20131127_164029_045_zps94164dd3.jpg&hash=559ca6a2e33edbf9f81bebd2eea0c3d7019a79b2) (http://s1350.photobucket.com/user/acarey3/media/IMG_20131127_164029_045_zps94164dd3.jpg.html)
What's the trick? :(
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I don't have the diaphragms like you have .
But from the post here from members that have, the plastic ring that secures the diaphragm to the slide needs to be heated up to get the diaphragm off .
I'm not real sure, but the plastic rings are difficult to get, the whole assembly, the slide and diaphragm and ring come already put together .
So be gentle in your removal process, or better yet, wait until someone with some experience with this posts about it .
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I bet you've the flat topped carbs.
The diaphragms are said to be non removable and have to be changed with the whole piston which is very expensive. I know some of us had succeeded in removing the plastic band, exchanging the diaphragm and re assembled back the plastic ring without breaking anything. I also know some people whid did destroy the rubber and the plastic band forcing them to spend $$$ at the dealer...
So wait for the expert advice from successful people.... And experience caution and delicacy.
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Can't recall how I handled mine, but can you pull those down towards the needle, instead of trying to lift them off the top?
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:'( I'm not feeling real encouraged here. I just looked at the parts fiche- $90 each! :o
Help!!
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Do you have flat topped carbs?
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Flat topped carbs, yeah.
I've done some more reading, and its said to put the whole slide in hot/boiling water and the nylons ring will "slip off".
I tried a heat lamp and the nylon ring loosened up enough to spin freely, but doesn't seem close to coming off. I'll try boiling water sometime in the next couple of days.
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Snowbum strongly advises against buying diaphragms directly from Bing. The Bing website has a category for BMW parts... Has anyone tried them?
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Original Bing parts are all I've ever used .
There have been reports from members here, that the aftermarket diaphragms are too thick and inflexible for motorcycle use and cause poor running .
This is one time I strongly disagree with Snowbum's reccomendations .
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Thanks Bob. Have you compared prices?
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Would advise against using Stromberg replacement diaphrams. They fit and are Ok as an emergency fix but they are thicker and change the way the bike runs.
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I always bought my diaphragms from Bing. I was warned away from the Strombergs by older, more experienced airhead owners.
It was a godsend once Bing started selling the diaphragms and plastic rings separately from the slide.
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I have replaced mine on my flat-tops, but I do not recall there being much of a knack. Or at least I cannot remember that I did anything particularly special....I certainly did not buy the whole unit - So I would not go down that route.
I probably carefully levered them off. Assuming the old one is definitely toast.
Orientation is critical
Good luck.
Rev Light
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Yep - if you are dealing with flat-top carbs, there is the plastic ring to deal with in R/R the diaphragms.
They snap off easily enough (just work a small screwdriver under them), and can be reused as long as they are within tolerance. (If they don't keep things sealed, they are out of spec...)
With new plastic rings I usually warmed them in boiling water for a few minutes before snapping them in place.
The diaphragms will have two locating tabs. One on the ID and one on the OD. They both have slots in the slide/carb body to be matched up. This ensures that the slide is in the carb correctly.
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Thanks guys, seems straightforward enough. I found another thread where the guy used a light to heat the ring, per a Bing tech's suggestion.
http://www.bmwmoa.org/forum/showthread.php?52288-1978-R100-7-Flat-top-Carburetor-Rebuild
Snowbum's site has a ton of great information, but reading it can lead to a lot of over-thinking. For me, at least. :P
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used a light to heat the ring
That was in my head, but I couldn't remember the source, so I didn't quote it!
The Bing Book is a great tool to have on hand, too.
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Snowbum's site has a ton of great information, but reading it can lead to a lot of over-thinking. For me, at least.
It's not just you.
Most references to his site usually come with a warning.
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Would advise against using Stromberg replacement diaphrams. They fit and are Ok as an emergency fix but they are thicker and change the way the bike runs.
I disagree, I put Stromberg diaphragms into the R100 and noticed no difference.
With the greatest of respect, when you think about how a constant vacuum carb works, the only possible difference would be in the rate at which the slides rise or fall due to greater 'stiffness" in the material.
I'm going to call "urban legend" on that one.
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Well, using a 100watt light bulb as a heat source for a minutes and the ring fell off. Perfect!
I cleaned up the parts and put the ring back on the heat for a few minutes while I figured out how the diaphragms gets aligned and prepared for reassembly. A couple minutes later, the ring was melted. :-[ I guess it's not nylon.
So I sent an email order to Bing for some more parts.
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So I sent an email order to Bing for some more parts.
Manual - $11.00! http://www.bingcarburetor.com/manual.html
Exploded Views
Tuning Tips
Tech Tips
Altitude Correction Charts
Jetting Specs
Jet Needle Charts
Miscellaneous Recommendations And Tips
This Manual takes you through all the circuits of the carb
Trouble shooting for specific problems
Order Today $11.00 postage paid within the USA
No, I don't work for them...
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Yeah that manual looks like a good idea. Except that I'll put these back on the bike and never have to work on them again! :D
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Would advise against using Stromberg replacement diaphrams. They fit and are Ok as an emergency fix but they are thicker and change the way the bike runs.
I disagree, I put Stromberg diaphragms into the R100 and noticed no difference.
With the greatest of respect, when you think about how a constant vacuum carb works, the only possible difference would be in the rate at which the slides rise or fall due to greater 'stiffness" in the material.
I'm going to call "urban legend" on that one.
We have had members here that have installed aftermarket diaphragms, LuckyLou in the UK got his from Motobins and had issues with his R65 running correctly .
There were two members here that purchased aftermarket diaphragms from a dealer in the Dallas / Ft. Worth area that had the same issues .
No idea who the manufacturer was, but the owners compared the Bing and aftermarket diaphragms and the aftermarket parts were notably thicker and less flexible .
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I disagree, I put Stromberg diaphragms into the R100 and noticed no difference.
With the greatest of respect, when you think about how a constant vacuum carb works, the only possible difference would be in the rate at which the slides rise or fall due to greater 'stiffness" in the material.
I'm going to call "urban legend" on that one.
Kind of hard to dismiss it when plenty of people have had problems with the diaphragms and the problems went away when they switched to Bing parts.
CV carbs don't have an unlimited amount of vacuum. If the diaphragm is stiff enough, it will keep the slide from lifting in it's bore. It's like putting a heavier spring on top of your slide. Get enough resistance and things get cranky.
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I'll put these back on the bike and never have to work on them again!
(https://bmwr65.org/smf/proxy.php?request=http%3A%2F%2Fwww.pbase.com%2Ftomfarr%2Fimage%2F85728833.jpg&hash=245e893554eb8908d9d033caad94d3b85889a27a)
But seriously, you will be working on these carburetors - for as long as you own the bike!
But you are right - I did not need the manual until I started switching parts around: Gen 1/Gen2.
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I disagree, I put Stromberg diaphragms into the R100 and noticed no difference.
With the greatest of respect, when you think about how a constant vacuum carb works, the only possible difference would be in the rate at which the slides rise or fall due to greater 'stiffness" in the material.
I'm going to call "urban legend" on that one.
Kind of hard to dismiss it when plenty of people have had problems with the diaphragms and the problems went away when they switched to Bing parts.
CV carbs don't have an unlimited amount of vacuum. If the diaphragm is stiff enough, it will keep the slide from lifting in it's bore. It's like putting a heavier spring on top of your slide. Get enough resistance and things get cranky.
BMW/BING CV Carbs have exactly the same amount of vacuum available to them as any other CV carb in the world.
Please note also that I was speaking specifically about Stromberg alternative parts and not about the unknown part being sold by someone in the USA or for that matter by Motobins in the UK.
However, at least as regards parts sold by Motobins, I have been buying parts from them since the early 80s and on the occasions that I have bought "pattern" parts form them I have never had a problem. Given that they are probably the biggest seller in the world of BMW motorcycle parts (after BMW themselves) I very much doubt that they would continue to sell a part that did not work in a functionally identical way to the original.
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Calm down, Tony. Opinions are like arse holes... everybody's got one. You're welcome to yours as are the other folks comments.
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It could have been a supplier issue, changed material and it didn't work very well, or changed the supplier of the parts .
I've seen it in the 37 years that I've been in aviation, change the supplier of a part and then have problems with them, even though they pass quality control, when they get out in real world use they don't measure up to the task .
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On the alternative carb diaphrams if we are talking all airheads across the range I've heard both sides of the story. Some say they are fine and some not.
There must be some difference with thicker diaphrams. I would expect there to be a slowing of the piston velocity in resonse to the throttle so that would mean a little extra richness possibly mostly a temporary effect like that provided by springs.
I guess that as all airhead Bings will not be identically tuned before diaphragm replacement then it's no surprise that experiences differ. They might even be an improvement for some.
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OK, so I've been musing on the aftermarket diaphragms since last night. Here are my thoughts about how diaphragm stiffness can be a problem for some people (manufacturing consistency?) in our Constant Velocity carburetors.
If the slide is held down (stiffer spring/diaphragm, more weight, etc.), but air demand is increased with an open throttle, then venturi speed will increase and pull more fuel from an equally open main jet in an accelerator pump fashion and probably richen the mixture a bit too.
However, it is not just the mixture that we have to worry about, but the air volume that makes it through the carb. I think this is the root of the problem that some people have had with the stiffer diaphragms.
A low slide will restrict how much air can get into the engine. While the air passing through the venturi can be sped up to some degree, there is a limit to how much this is possible (otherwise we could feed our airboxes through high velocity pinholes and we wouldn't have a variable venturi in our carbs). It becomes a problem of fluid (air) drag. For the sake of simplicity, consider the venturi cross section a perfect circle. As the radius increases the drag (circumference) increases linearly, while the volume is can pass (area) increases exponentially. A slide that is too low can be forced to breathe more via higher velocity, but it breathes less efficiently (and probably is more turbulent too) and there is a limit to how much it will let by since the engine can only pull so hard.
If the diaphragm stiffness (or any of the other variables) goes past the tipping point, the engine will not get enough air through the venturi bottleneck, no matter the mixture.
The automotive engines with the Stomberg carbs are pulling a whole lot more displacement through the carbs, and produce manifold vacuum more evenly (2-4 cylinders per carb), and with a greater manifold air volume to buffer the manifold vacuum level. I think this is why a stiffer diaphragm works fine on those bigger engines, whereas the BMW boxer pulls a small amount of air through a small manifold at 1/2 to 1/4 the number of intake strokes per revolution, and thus has less available low pressure to keep the slide lifted by the time the next intake stroke comes around.
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AlfromNH, please keep us refreshed with your work on these flat tops...
I did change (the diaphragms) mine a year ago but for some reason, the right carb just kept loosen after a while... after a few more tries, I ended up replacing my carbs for "non flat" units, fortunately, I got them quite cheap, but I still have the old ones just in case...
Thanks!!
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Hello !
I did change my diaphragms a little more than a year ago. I bought them from BMW 3 at a time because I like to have one in the spare box in case something goes wrong on a Saturday afternoon...
Last month a friend of mine asked for help on his carbs (he also own an R65)
I gave him a shopping list with 2 new diaphragms from BMW and, guess what ? theirs are stiffer than mine ! and wear the same part number. So I guess BMW has switched supplier or has fired the quality control department...
The bike runs fine (no comparison before and after.... if you saw what we find in the carbs...) so I wonder if it makes a lot of a difference.
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but for some reason, the right carb just kept loosen after a while...
Did you replace the white rings with new, as well?
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AlfromNH, please keep us refreshed with your work on these flat tops...
I'll be happy to, although I won't be able to report anything about the performance until I get the bike together in the spring.
I'm assuming Bing was closed for the (US) holiday weekend, I hope to hear from them today.
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Hello Rob!!!
Yes, we did change the white ring... the left carb actually works perfect, but the right one kept loosing the diaphragm and we just gave up!!!
Now, I got a set of "hat-top" carbs very cheap, so I decided to work them out instead, but will be redoing my flats some day, just to have a spare...
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I ordered 1 white ring from Bing for $6.41. I also ordered the manual. I ordered jets and needles from the BMW dealer. BMW prices are cheaper than Bing's, which I found somewhat surprising.
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I gave him a shopping list with 2 new diaphragms from BMW and, guess what ? theirs are stiffer than mine ! and wear the same part number. So I guess BMW has switched supplier or has fired the quality control department...
The bike runs fine (no comparison before and after.... if you saw what we find in the carbs...) so I wonder if it makes a lot of a difference.
Absolutely none whatever. There is a surfeit of "power" available in the vacuum system of the carb. If you want to amuse yourself, calculate the area that is exposed to vacuum and then work on (for the sake of example) a pressure of 14psi. The diaphragm being a "bit stiff" is not going to stop that slide doing what it is supposed to do. And within sensible limits there will be no difference between the thickest aftermarket diaphragm and the one you knock up in an emergency out of a gossamer condom (but don't used the ribbed ones, you would not want your R65 to get excited).