repairing rubber carb diaphragm--glue?

I found a tear in the black rubber diaphragm of my left carb. Hopefully
that is what is why I'm not getting much power out of the left cylinder.

The tear is about a half inch long and runs alongside the edge of the
piston and is about 1/16" from the piston

Does anybody know a good way to fix the diaphragm?

Maybe my question amounts to asking for a glue that is good for fixing
rubber. I tried some blue Permatex but it did not stick well to the rubber.

 

There are specific 'rubber' glues but I have no idea if this will work
as everybody I know with this problem has replaced the piston. Nor do I
have a specific product to recommend.

Keep in mind that if you have one crack, the seal is probably done for
and if repaired, will only crack in another place maybe leaving you
stranded.

 

If you have some very thin natural rubber sheet, cut a piece and glue
it to the underside of the diaphragm. Air coming up under the diaphragm
actually lifts it, but most riders would probably think that vacuum
sucks the diaphragm up. TOG was talking about "flexible" superglue last
time this question came up, but I used a piece of a raincoat I'd been
given in Beijing in lieu of change and I glued it on with black rubber
cement...

 

I've used them. They are, indeed, superb. Excellent product, excellent
service.

 

Flexible superglue works.

 

Thanks. It seems like maybe they have moved to:
http://web.ukonline.co.uk/nrp-carbs/manufac.htm

 

Scratch that email address. My mail to that address just bounced.

 

Do you happen to have their email address? Could you say about how long
it took and how much it cost?

 

Google for their email. Or they advertise in CMCM.

As for the time - it took about a week, door to door. Cost was (IIRC)
about ukp30 per carb.

 

They seem to have left a trail of derelict websites. My email to the
following hasn't bounced yet:

http://www.cameron-site.co.uk/nrp/index.htm

 

I've seen alot of replies to this thread (not all), but one thing I
thought would help on fixing it is how about replacing the torn one with a
new one? are they so expensive that it becomes cost prohibitive? Just a
thought.... good luck

Fwed

 

The diaphragm is integrated with a piston (aka slide). Here is the item
at partsfiche.com:

16022-369-004 PISTON SET, VACUUM 81.99

I believe that that is NOS, and there are shelf-life issues. No, I
don't believe anybody makes these new. A pair of these carbs goes for
$60 once a week on ebay, but it's hard to tell what you are getting.

From my armchair I claim that the carb designers could have made the
diaphragm easy to install to the piston and sold the diaphragms
separately for $5 each. I don't know what fraction of these bikes have
been discarded due to bad diaphragms but I would bet it's more than 10%.

 

Basically, if you're talking about OE, yes.

Old airhead BMW units are the exception.

 

Thanks. Not sure I understand your method. I believe you are saying
that you take a piece of a diaphragm from another carb and use it as a
patch. Then exactly what adhesive do you use? I don't have much room
for trial and error on this, so I would appreciate as much detail as
possible.

 

I think he means he went rummaging through old carbs to find an
undamaged diaphragm or two.

Like I said - flexible superglue works well, but when the dias are that
old, you tend to get new splits and holes developing. Best solution is
replacement with new items.

 

I wouldn't.

 

if there's ANY way to get another one, do it. you may have to buy another
used carb.
there's no really good way.
good luck, sam

 

And I would expect that better materials are available now than in 1976.

 

Absolutely.

 

Okay, I got my slides with new diaphragms back from NRP Carbs and
Diaphragms. Definitely the blown diaphragm was the cause of the left
cylinder not firing and of the fouling of the left sparkplug.

The new rubber looks good and new and strong. Cost for rebuilding both
slides including shipping both ways was about $130, and the job took 21
days including shipping time. Apparently they received my slides on a
Monday and got them back out the door on Friday.

I can't say that they were responsive to me as a customer. Several of
my emails and phone calls were unanswered. I found myself wondering
whether they had received the slides and how they would be shipped back
and how I was going to pay. I don't know why they don't post a
descriptive list of shipping options to the U.S. or at least provide
such info upon request---they don't seem to be putting much work into
their website or email.

The Royal Mail tracking number followed the package to JFK airport but
not within the U.S. NRP insured the slides for GBP 70, which was the
cost of the work they did. But that didn't include the cost of
replacing the slide cores, so I would have had to pay the cost of the
cores had the package been lost.

Anyway there was a good outcome. To anyone who can tolerate the
turnaround time, I would generally recommend using NRP instead of buying
NOS.