Replacement CV diaphragms

[slmjim n Z1BEBE]

We received a couple of good responses to a question we posted on another forum re: replacing CV diaphragms. No personal experience with either yet, just sharing for those who may be interested.

https://www.carburetordiaphragms.com/

http://jbmindustries.com/Dimensions.html


Good Ridin'
slmjim & Z1BEBE

[Bob H]

Yeah, those look like more reputable providers than the ones I was looking at earlier this year.
Ultimately I paid through the nose to get the OEM ones from Partzilla, because they were still available and who knows when that may dry up.



$133 EACH (x 4) but that includes the slide, not the needle. Diaphragms bonded to the slide.

The flaws in my diaphragms were small slit in 2 of the 4, only visible when "pulled" against a light background. I didn't see them at first. Only 38,000 miles, likely age related.



I already had so much labor into the carbs, I bit the bullet on the OEM parts.

[Willie]

A few years back, I found a guy online that was making them. Had nice little business going. I regret not holding on to his contact info because the ones I bought from him were top notch.

[Bob H]

A few years back, I found a guy online that was making them. Had nice little business going. I regret not holding on to his contact info because the ones I bought from him were top notch.

Was it JBM Industries?

They are the 2nd link provided by the OP (slmjim & Z1BEBE)

When I was researching diaphragms they were mentioned in a lot of various motorcycle forum threads going way back.
They have a mention of ethanol affecting vintage diaphragms, and mine were definitely looking like the image below - even the 2 of 4 that did not have splits were all buckled looking.


Apparently JPM uses a type of rubber that may withstand Ethanol better than the OEM parts

What is TSR compound? What kind of rubber is it? What are the qualities of it? Is it
indestructible?

TSR compound is a patented rubber compound that only JBM Industries is using for
the manufacture of high quality fuel resistant rubber parts in light sport aircraft and
vintage motorcycles.  ( Working -10 to +275 deg. F )
The qualities of the TSR rubber are that it has high fuel and chemical resistance so
works well with fuels that contain ethanol.  It also is very resistant to heat, ozone, and
age cracking. Age cracks are the small surface cracks seen in old rubber that can be
seen with just a slight bending of the rubber. Usually you will see many of them, and
they will not be very deep, but they do weaken and soften the rubber, causing more
flexing and so more age cracks.
Many elastomer's get age cracks, and on some rubber, such as natural rubber they
might look bad but cause little weakness. On other types of rubber they can degrade
and weaken it quite a bit.
To check for age cracks, it requires a small amount of bending or flex to see them
open up. Rubber parts should be checked for age cracks frequently.
TSR material is not any stronger, or indestructible, than other rubbers. 
JBM Industries uses two types of this rubber with different frequency response,
depending on the part we are making. It does have a bit different "feel" to it and
has a very high specific gravity, so it is heavier than other elastomer's .
http://jbmindustries.com/

[Willie]

I believe so. GREAT detective work!
Thanks!

[Pete in PA]

Now you have me paranoid about mine.  Of course I looked at them last winter, found no holes, tears, etc.

Got me looking at what's available.  4 complete from Ebay, several sources, cheap price.

Can also get the rubber only.  2 types.  1 where you cut off the plastic rings and another where you put the new rubber back in between the rings. I'd go that route.
You'd think that the weight is also critical to correct function along with spring force, thickness of rubber etc.

92 750 NH.

[mollusc]

I got a set of new rubbers only for my 700S several years ago.  I could not for the life of me work out how to get the old rubber off the slides, and ended up destroying one of them in the process.  The rubber seems to be permanently bonded to the metal, so I'm not sure if that is a viable route for that bike.  Can't comment on how it might be for other Nighthawks but I imagine that the internals are probably pretty similar across all the Mikuni carbs.