BS34 diaphragms - repair? / replace?

[Paulrxs650]

Hi,
Just stripped the carbs down as part of the build. Not bad inside apart from the usual muck. However, the diaphragms have, what appears to be very small areas of de- lamination. They don't appear holed but I don't think they are up to scratch, so:

Can they be repaired?

If not, where can they be sourced at sensible prices - a quick look on eBay and its £60 +

Thanks

Paul

 

[gggGary]

JBM Industries seems to be the best, they ship internationally.

http://jbmindustries.com/Yamaha650.html

 

[jetmechmarty]

The only issue I have with the JBM diaphragms is that once you use them, you can never go back to anything else without replacing the slide. Then again, that shouldn't be a problem, should it?

 

[xjwmx]

JBMs reportedly are just rubber rather than rubber over cloth, which makes them weaker than stock. I would repair the originals as long as possible. There is a material called "Sportsman's Goop" which would probably be good to put over holes. It's more flexible and stickier than Seal All (from the same company, I think). Yamaha replacements are out there still, for more $, if you look hard enough.

My diaphragms were like what I think you describe and I borrowed liquid electrical tape from a friend because that's what we had on hand and they are at least no worse than before! There were tiny areas of bare cloth visible but no actual holes apparent.

 

[rebel542]

You might want to look for some 38's.

 

[weekendrider]

If you lift the slides and they don't fall with the bled hole covered......
or do they?

 

[Paulrxs650]

Hi, they dont fall which indicates that they are sound ( for the moment ) so it may look like a repair, to prolong longevity?

 

[Paulrxs650]

Just checked and JBM are out of stock at the moment til December 10th. They say for the 34's you use the original slides too.

 

[jetmechmarty]

YAMAHA XS650 XJ900 XS750 XS1100 CARB SLIDE DIAPHRAGMS

This is another option also out of stock until 12/12.

or

BRAND NEW CARB SLIDE DIAPHRAGM YAMAHA SR250 XS650 XS650S XS400 XJ400 Mikuni BS34

I like the tutorial in the eBay listing. Have a look!

 

[Paulrxs650]

Yeah - I saw that earlir today - very specific for ebay - good sign of a good seller though!

Everyone must be waiting for the same manufacturer!

 

[peanut]

I posted the JBM link last week as they looked really cheap . I think they are made to aircraft spec so should be top quality.I think I'll order some myself when they are back in stock.

 

[weekendrider]

Not that I've done it but those that have say a little nail polish will hold the slides from turning.
You want the bleed hole for the slide to the front iirc.
I think this is covered on their web site?

 

[Paulrxs650]

Never tried that one, canny tip though!

 

[gggGary]

Yes I looked at the JBM website again and it is very thorough. A lot of suppliers could learn some lessons in service and support from what they posted. I picked up a couple of good carb tips too. Crazy glue used VERY sparingly seems to be the glue of choice.
I have watched replacement bike carb diaphragms start as a minor side line, to it being a significant portion of their business. (I think) There's a nice page on how they find, modify, and rebuild old rubber parts presses.

 

[bluebikerblan]

Replace with JBM's as available. Hot item! good value. excellent DIY repair design. Have them available when OEM diaphragms fail. Replace as a pair they need to function identically. One of the reasons glue/gunk repair does not work well!

 

[Paulrxs650]

As soon as they're in stock I'll order!

 

[xjwmx]

One of the reasons glue/gunk repair does not work well!

You've never tried a repair. But you are involved with JBM gunk somehow. Makers of the useless 34 carb holders with no vacuum port.

To the OP: read up on JBM diaphragm expected lifetime and issues with the piston turning. When I actually make a suggestion here it's a serious thing intended to benefit somebody else.

 

[gggGary]

xjwmx The only expected lifetime reverence I can find is on JBMs own site they started out with aviation (ultralite) parts and tend to be very conservative about making untested claims. I like that in a vender! Yes you have to index the slides a sptt of glue holds the orientation. I found no user problems with any of his diaphragms only good reports. You you know of a beef prove it. Yes he was unhappy with the vacuum ports coming loose, so quit putting them in. Many carbs have their own vacuum ports and there are other ways around it. I have not purchased or used JBM parts but again have heard nothing but good about his products. Compare to mikesXS rubber parts reliability?

 

[xjwmx]

xMany carbs have their own vacuum ports and there are other ways around it.

You know they're intended for the BS34, and you know that you can't sync those carbs without a vacuum port. Unless you want to try to do it by ear.

The lifetime issue is I read a post somewhere that said they were developing holes after a couple of years. I didn't bookmark the post so I can't easily produce it. And I don't know anything about the veracity of that post. But I have read they are not rubber coated cloth. All these parts are rubber coated cloth when they're genuine Yamaha.

I will grant they are probably a step up from Mikes rubber, though I haven't used either, just read the reports.

I do not have a "beef". I am hesitant to replace genuine Yamaha parts that are repairable with something else, especially something else made with constraints, evidenced by lack of ability to provide a vacuum port. Basic. And evidenced by lack of ability to make from durable rubber coated cloth, more complicated than rubber alone.