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Old 08-22-2013, 08:22 AM   #1
RayB OP
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What Kinf of Life Do You Get from Your Diaphragms?

I also posted this on Boxerworks forum.

I'm curious as to what other people see with regard to diaphragm life in years, not miles before you see degradation.
Then what type degradation do you see - stretched diaphragm, hole, tear?

In your reply please tell us what % ethanol is in your typical fuel too.

I appear to be getting about 3 years before diaphragms get stretched out making cable balancing for 3500 rpm next to impossible for repeatability.

I typically run what's available near me, 93 octane ,(RON+MON)/2, with 10% ethanol....that's what we have near me and I'm in the Chicago fuel market area.

Do you find your diaphragms to be stretched or distorted when you change them out? That's what I'm seeing even though acceleration wasn't sluggish I was getting vibrations from imbalance. Never have had a tear or pin hole.

I've seen the same thing on a lawn mower with Briggs & Stratton engine with a diaphragm...had to change it once per year when it started running like crap I knew it was time. I blamed it on ethanol vs. the diaphragm material.

I wonder if the hydrin diaphragms as sold by Motobins would be a better material
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Old 08-22-2013, 09:11 AM   #2
Stan_R80/7
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I am getting 35 years so far. Still on the original diaphragms. I have replacements.

My understanding is the diaphragms provide a seal to allow a vacuum to form on top of the piston. The diaphragms are still pliable with no holes or tears and allow the piston to move. So, they operate as intended.

It is likely that changing them may improve carburetor operation slightly - but this is one of those situations where I am not so much of a perfectionist. Well, that, and after 35 years I am now curious how long they can last? Certainly, YMMV.
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Old 08-22-2013, 09:14 AM   #3
100RT
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Mine have been in for several years and were changed out during a rebuild at the time, just because I was in there. I tried the Motobins items and thought they were on the stiff side and took them out.

Are you buying from BMW or Bing or who, there is a difference.
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Old 08-22-2013, 09:37 AM   #4
Gian4
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Hold on I'll ask the wife.
Gian4.....to easy but I had to say it.
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Old 08-22-2013, 09:48 AM   #5
Rinty
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That only took 4 posts...

Rinty screwed with this post 08-22-2013 at 12:24 PM
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Old 08-22-2013, 10:51 AM   #6
RayB OP
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Quote:
Are you buying from BMW or Bing or who, there is a difference
Bing
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Old 08-22-2013, 11:05 AM   #7
globalt38
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Quote:
Originally Posted by Gian4 View Post
Hold on I'll ask the wife.
Gian4.....to easy but I had to say it.
Great - thanks! Now with this in my mind both Stan's and 100RT's posts just sound - wrong...
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Old 08-22-2013, 11:46 AM   #8
danedg
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I just replaced the diaphragms at 70,000 miles. The bike seems easier to adjust and it runs better.
I'm also going to replace the needle jet and the jet needle as my mileage currently sucks. Those two parts wear out and ruin your mileage.
Check your floats.

For some reason BMW sells better parts at the same price.
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Old 08-22-2013, 11:52 AM   #9
RayB OP
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Quote:
Those two parts wear out and ruin your mileage.
Check your floats.
I'm good on jets, jet needles, needle adjustments, float levels.
The only thing wrong was floppy diaphragms.

I'm looking for the number of years people go before noticing diaphragm degradation [ original post ]
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Old 08-22-2013, 12:45 PM   #10
Rob Farmer
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Quote:
Originally Posted by Gian4 View Post
Hold on I'll ask the wife.
Gian4.....to easy but I had to say it.
Boom Tish!
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Old 08-22-2013, 04:25 PM   #11
supershaft
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100,000 + miles plus. Your issues sound like you use spray carb cleaner on your carbs? That stuff melts and deforms diaphragms.

Same story with floats and jets other then the jet needles and needle jets and they barely wear at all in the earlier model carbs that have the spring loaded clip versus the later carbs' C clip.

There is a difference. Get BMW diaphragms.
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Old 08-22-2013, 04:27 PM   #12
Kai Ju
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Quote:
Originally Posted by Rinty View Post
That only took 4 posts...
I'm surprised it took that many...

Also, count yourself lucky. If you had a Japanese bike older than 10 years you'd be hard pressed to get new slides, which is what you have to buy to get the diaphragms, they don't come separate. Big money if you can find them. Upwards of $ 70+ in most cases.
One of the reasons I like the late 70's early 80's vintage Honda CV carbs that had a labyrinth seal instead of a diaphragm.

Kai Ju screwed with this post 08-22-2013 at 04:58 PM
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Old 08-22-2013, 05:38 PM   #13
RayB OP
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Quote:
Your issues sound like you use spray carb cleaner on your carbs
I do....on teh carb body and passages after they've been disassembled and the diaphragms never are exposed to the spray.

Are BMW diaphragms and Bing ( Bing USA) diaphragms not the same?
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Old 08-22-2013, 06:13 PM   #14
100RT
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Quote:
Originally Posted by rayb View Post
i do....on teh carb body and passages after they've been disassembled and the diaphragms never are exposed to the spray.

Are bmw diaphragms and bing ( bing usa) diaphragms not the same?
nope
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Old 08-22-2013, 06:24 PM   #15
boxerboy81
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There are diaphragms and there are diaphragms.

BMW/nitrile
BING
Stromberg
Motobins/Hydrin


Motobins describe their oem offering as:
Quote:
These high quality diaphragms are used by ROVER and are approved by SAAB. Made from Hydrin they last longer than Nitrile ones and are equivalent to the originals. UKP18.50 (40mm carbs)
Motobins describe their "pattern" offering as:
Quote:
These high quality diaphragms are used by ROVER and are approved by SAAB. Made from Hydrin they last longer than Nitrile ones and are equivalent to the originals. UKP8 (40mm carbs)
Motorworks sell their diaphragms @ UKP7.20. Guess they're the pattern sort from Motobins, which according to the online description might be the same as the more expensive "oem" Motobins offering?
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