How To Repair A Torn Rubber Diaphragm

Looks like this is going to work ... so, I'll "Get it out there"
Diaphragm Rubber Repair:

Clean the Rubber with isopropyl alcohol.
Apply MASKING TAPE to the OPPOSITE SIDE of the Repair.
(Holding the tear together > Perfectly.
Cut a small Funnel to act as a form.
Tape the Rubber to the Form.
Make sure Rubber is not buckled or wrinkled.

Salvage some "Repair Material"
(I used a small section of Material cut from a Nylon Windbreaker)

Cut-out a PATCH of Repair Material to COVER the TEAR.
Coat the Rubber over the TEAR with a thin coat of LIQUID Electrical Tape.

>> Quickly apply the Patch with TWEEZERS and "Iron-Out" any Air Bubble or wrinkle with a BIC Ball Point Pen (Cover and Blunt End)
Smooth-out Patch.
You don't get much time to do this.

Once Dry:
Apply 2nd Coat of Liquid Electrical Tape.
When 1st side is dry ... repeat process on other side of Rubber ...
BUT
Don't Stick Tape on the Repair ... Just Smooth the Diaphragm Rubber Out.

November 23, 2009
"The RickCoMatic Patch"

"If I can't fix it. ... it ain't broke."
--- Will Rogers
I second Rick's approach to this problem. Ageing bikes and ageing rubber diaphragms in the carbs will be a problem at some stage or another.
It's amazing how long they have lasted in that environment in which they operate.

I had a few pinholes in a couple of mine and I used the spray version of the liquid rubber. I dabbed a little on the pinhole and then when a little dry I lightly sprayed the rubber diaphragm (with the rest of the plunger mechanism masked off).

So far I have put on around 20,000kms since doing so and cannot detect any problems in that area. I haven't had the carbs apart since but maybe in the next year or two when I give the bike a good once over service I'll check and report.
I'll back you up on that,
but suggest another material.
I recently did the diaphragms on my Venture which had perforations on all four, and I used Orange Goop hand cleaner as the pre-clean, and used Ether or Starting Fluid as the final cleaner, to completely de-grease the surface.
I did not use masking tape, but that's a nice touch there.
I used Liquid Electric Tape as the glue, and I used Nitrile Gloves as the filler material, available at Harbour Freight. An important point, the filler should be on the high pressure side, the bottom, not the top.
The idea is that the filler material has the same flexibility as the original material, and is gasoline proof.

Hey, you guys know how much these things cost ???
I used Silastic to repair my pinholes....seems to be working fine. I don't think the diaphragm is "immersed" in petrol is it?
By the way how does the vacuum work??? I see a small hole just near the needle but with the top of the carb sealed I'm baffled as to how they operate...anyone got a link to a plain english explanation on how CV carbs work?
The underside of the diaphragm is exposed to outside air pressure.
The top of the diaphragm is open to the carburetor throat (because of that small hole) and has the air pressure inside the carburetor.

As the air moving through the carburetor speeds up it's pressure drops (same thing that makes an airplane fly). Because of the hole in the slide the pressure on top of the diaphragm drops too.

Since the pressure below the diaphragm is higher than the pressure above the diaphragm lifts the slide against the spring.

As the slide lifts up the passage in the carburetor body is made larger. Since it's larger the air speed drops and the pressure increases. When everything is in equilibrium the slide stops moving.

This type of carburetor is called "Constant Velocity" (CV). The slide keeps the air speed through the carburetor relatively constant.
Much obliged MiCarl! Seems like a very clever design!!
I had a tear in one of my diaphragms. I used vulcanizing fluid (the stuff that applies patches to bicycle inner tubes) and it's been quite wonderful.
"Clever" isn't quite the word I'd use.
Although when everything is functioning PROPERLY they do work quite well, and neatly solve the problem of cleanly regulating fuel-air mixture over a WIDE RPM range; independent of (but in response to) throttle opening.

It's that "functioning properly" caveat that makes them a PIA. But on the other hand, I don't think Yamaha had any idea that we would still be riding and maintaining these things 25+ years down the road.
this site really is amazing and without trying to sound "mushy"
i don't know what the rest of us would do without the skills
and knowlege you guys pass on!
thanks to all of you ( and i'm speaking to everyone that adds
to these threads).i've always been concerned about damaging my diaphrams during cleaning, so much so that it takes FOREVER to polish
the slides for fear of even handling the darn things.
i wont be less carefull now but much less paranoid! thanks!
The Pistons aren't in need of the Polishing as much as The BORE where the Piston fits does.
The aging and oxidizing process which causes Aluminum to dull and be coated with a dusty glaxe affects the way the Diaphragm Piston to freely travel.

The BORE needs a scrubbing and a cleaning.
I scrub the Bores with ScotchBrite Medium Pad strips.
Remove the glaze.
To increase your performance ... Polish the Bore.

Scrub:

Polished: (Buffed with Rouges for finish)