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Replacement carb slide diaphragms 6 years 1 month ago #15697

  • Craig
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Hello Zed Thirteen. I bought a spare set of those exact diaphragms....and yes....they are not as soft and flexible as the originals. I was disappointed and doubt I will actually try them out any time soon!

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Replacement carb slide diaphragms 6 years 1 month ago #15714

  • zed_thirteen
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Thanks Craig,
1980 KZ1300 B2 Touring/A2
1990 ZZ-R1100 C1

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Replacement carb slide diaphragms 4 weeks 17 hours ago #31151

  • Kawboy
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Raising this topic again to discuss the current availability of diaphragms for the throttle pistons.

I went on the hunt for replacement diaphragms and found 2 vendors marketing on EBay that offered aftermarket manufactured diaphragms. Both vendors are located in the United Kingdom. One is Legend Motorcycles and the second is "djin1378". I contacted both vendors and asked 2 specific questions.
What material are these diaphragms made of? Nitrile or Viton?
Are these diaphragms reinforced with a cloth like material?

Neither vendor would answer the questions specifically.
Legend motorcycles answer- "I've sold over 600 of these diaphragms and haven't had a complaint yet."
Djin1378's answer- Mine are the best quality available on the market. You could test one diaphragm if you wish and if you're not happy, return the remaining 2 and I'll refund you for 2 of the 3."

Legend Motorcycles sells the diaphragm by the each.   $17.91 USD + shipping
Djin1378 sells the diaphragms in sets of 3.  $74.99 USD + shipping

I currently don't need any diaphragms but knowing that the diaphragms are a consumable item, thought I should probably pick up a set for future use and at the same time investigate /review the current products available. I thought I would start with the single diaphragm from legend motorcycles and I ordered one. 3 weeks later, I have it .

My first mistake- I picked up the mail and found the envelope from the UK with the diaphragm and headed home. When I got in the door, my wife Pat told me that it was coffee time and started making the coffee. I, in the meantime, cut open the envelope and pulled out the diaphragm and look at it. Knowing that as per the previous post on this topic, some of the European made diaphragms were thicker and that the throttle pistons didn't react the same as the original diaphragms, I felt the diaphragm and was surprised at how subtle the material was. thinking that this was not a problem at all, I was really happy with what showed up.
Now I'm sitting down having coffee and as usual, pulled out the computer and do what I usually do, login to and check for posts , then go running around the internet looking at motorcycle topics. This time I thought , you know what, I should just order 2 more of those diaphragms and I'll be all set. So I did, then something in the back of my head as "Why don't you have a really good look at the new diaphragm while you're sitting here having coffee" . so  I go grab the diaphragm off of the kitchen counter and take it back to my seat in the family room. I no sooner sit down when I noticed that unlike the original diaphragm, you can't see the cloth reinforcement in the membrane. Oh no. Tried stretching the membrane and yes it stretches easily like a rubber glove. Well, I don't like that.
So I had ordered the 2 diaphragms at 9:38am my time and at 9:42 am , 5 minutes later, requested a cancellation of the order. At 10:21 I get a notice that the cancellation request was declined because the vendor had already shipped the item and it had been picked up by Royal mail and it was on its way. REALLY !!
I sent off another message to the vendor regarding the purchase and asked about the cancellation decline. Their response was that they just managed to package it and get it off and shipped minutes before the scheduled pickup and all of their customers really appreciate the quick response when shipping AND you'll be really happy with the product. everyone else who bought these diaphragms are happy.
So I'm declaring Bullshit here. I don't care how good you are, receiving an order and shipping within 5 minutes- I couldn't read the order in 5 minutes never mind pull the stock, package it, label the package and hand it to the shipper in 5 minutes.
So I'll be receiving the 2 diaphragms in a few weeks and that's that.
Now back on topic-
My concern about the lack of reinforcement is that these diaphragms are now relying on the elastomer to do the work of raising the throttle pistons and rubber reacts differently when warm or cold so knowing that the pistons also act on the metering needle, depending on the temperature of the diaphragm, the fuel mixture will vary. With the stock diaphragm, the work of lifting the throttle piston is done through the reinforced cloth and the only purpose of the rubber coating is to air seal the diaphragm.

Both of these vendors have sold over 1000 diaphragms in total and these diaphragms are unique to the BSW32 carb which is only used on the KZ1300 so I find it interesting that there is a lack of information about the diaphragms in our site. Are other KZ1300 owners working on another site and not active on our site? What am I missing?

Knowing that these diaphragms will react differently than the stock ones, can the jetting metering rods be worked with to overcome the downfall of these diaphragms?

How many times has the topic of jetting come up and those that rejetted based on another post about what another member used, caused issues. if the diaphragms are not a constant, then they are a variable and that complicated things for those who are not engine tuners.

Are there manufacturers out there that can manufacture diaphragms as per the original design and not make crap that the average user can buy with confidence?

I get so disillusioned with the crap that's made available these days. We all used to complain about Chinese garbage and yes there probably still is a lot of garbage coming out of China and India and if it weren't for sites like ours to share thoughts and advice, we'd all be lost.

Please, if you have experience with any of the aftermarket diaphragms, post your thoughts here.

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Replacement carb slide diaphragms 4 weeks 16 hours ago #31152

  • Daro
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Hi all, yes I too have such new diaphragms somwhere in the drawer. If you change only one diaphtagm and monitor the color of the sparkplug in two of the cylinders being feed from it than you can evaluate how it works just by comparison. What can happen is the heavier and spongy diaphragm don't lift the piston as it schould and so mixture will be leaner.
I never installes theme so cant help in any other way, but they are also with out the fabric inside and little thicker than the original.

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Replacement carb slide diaphragms 4 weeks 13 hours ago #31153

  • dcarver220b
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Nachfertigung vom nicht mehr lieferbaren Vergasermembran mit der Ersatzteilnummer 43028-1014
Passend für alle Vergasermodelle 
Reproduction of the no longer available carburetor membrane with the spare part number 43028-1014
Suitable for all carburettor models

His stuff is much better, across the board, than eBay sh@#$t IMHO of course :)
The following user(s) said Thank You: biltonjim

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Last edit: by dcarver220b.

Replacement carb slide diaphragms 4 weeks 12 hours ago #31154

  • scotch
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The need for these was due to a Set of carbs I bought from an ebay seller (US).  Advertised (implied) as  simply needing a cleaning and set-up; it was a gut-punch to discover the actual diaphragm(s) were missing (from the hardware).  A brief word to the seller and a suitable resolution was agreed upon.

OEM diaphragms in usable condition are now very rare !  There's legitimate concerns regarding the Aftermarket ones and I agree. 
 According to the Sellers there's hundreds out there.......... with no problems ! [justify]If they's the best kept secret. 
"Thanks for the "feed-back" 
[/justify]Needless to say:  I started "smashing eggs" ! 

My diaphragm construction has a fabric core like the OEM's and have Nitrile on each side. Like OEM's, by comparison, they are every bit as subtle and don't stretch ! 
A "static" test - lifting the slides with a finger and releasing,  has the assembly dropping immediately.  
 Diaphragms do not come in contact with raw fuel so I have no concerns about the nitrile.   And,  no......not concerned about "fuel-bowl vapors" either.  Below the diaphragms is fully vented and this "air" is constantly being vented by the up/down travel of the diaphragm.
Over the past two years I've  been progressively "tweaking" my original carbs.  52 MPG with no apparent loss of performance......  so this current set will get the same Mods plus my diaphragms and I'll see what I can achieve from these.
Weather-wise, it's going to be 2 more months before my bike is on the road.  I'll know immediately if my fabrications work.  

1980 KZ 1300 sr# KZT30A-009997
Always High - Know Fear !

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