gas resistant (proof?) adhesive

As a last ditch effort to get my 305's original carbs running properly, I need to glue my aftermarket diaphragms to the vacuum pistons. OEM rubbers are stupid expensive (150 each) if you can find them at all, and I'm not anxious to buy used ones. Glueing them is NOT recommended by the maker but the problem is they are slightly too large in diameter so a dab of super glue to keep them in place won't do a thing. They need to be sealed and adhered all the way around. So, barring any better suggestions I was planning to use something like Seal-All, which is gas resistant but not gas proof and probably won't last very long. You're also not supposed to use silicon, and Seal-All is silicon. This is otherwise the end of the road for these carbs and I will have to buy Mikunis because I'm tired of these carbs.

jbm industries has affordable diaphragms for some models. diaphragm adhesive mentioned here and elsewhere: gorilla glue or seal-all. possibly super glue. such as loctite 401 which came with a dorman cv boot kit that I installed on my car.  the gorilla glue is a cyanoacrylate super glue

I would try this stuff. I use it for many applications. it is very sticky stuff so you would haves to figure out how to apply it without getting it all over the place. But worth a try.
www.wholesalemarine.com/mercury-mercruis...IEAQYBSABEgIypPD_BwE

Polysulfide sealer is the only stuff I'd trust.  It's used to coat aircraft fuel tanks and isn't affected by fuels.  It's expensive, though.  It's a two part material, so it's effectively a one time shot since you mix all the material at once.

This said, I would not use it to seal diaphragms unless a last resort.

When I disassemble a carburetor, the diaphragm is usually dry. I would think fuel resestant is good enough.
Question: Does fuel air mixture get up to the diaphragm, or only clean intake air?

Under normal circumstances I would only expect fuel "vapour" to reach that point

H1Vindicator wrote:

jbm industries has affordable diaphragms for some models. diaphragm adhesive mentioned here and elsewhere: gorilla glue or seal-all. possibly super glue. such as loctite 401 which came with a dorman cv boot kit that I installed on my car.  the gorilla glue is a cyanoacrylate super glue

Some measurements needed to confirm, but JBM seems to sell diaphragms for the 305.  This would be a no-brainer option to me.

Yes I would go with JBM first if they have them for your carbs. They make great diaphragms.

H1Vindicator wrote:

jbm industries has affordable diaphragms for some models. diaphragm adhesive mentioned here and elsewhere: gorilla glue or seal-all. possibly super glue. such as loctite 401 which came with a dorman cv boot kit that I installed on my car.  the gorilla glue is a cyanoacrylate super glue

 

I have the JBMs. They are too large. They even replaced my first set at no charge same problem. They will drop right off the piston. I'm very doubtful a super glue will seal the gap properly so I'll have to opt for something  else. As long as the Seal All won't damage my engine somehow if it degrades, its a cheap risk

If you can stomach the shipping and waiting the below company in the UK will fit replacement diaphragms to your slides ready to install for approx $40 each plus shipping (maybe somebody in your part of the world offers the same service ?)

NRP motorcycle carburettor repair specialist

Wookie58 wrote:

If you can stomach the shipping and waiting the below company in the UK will fit replacement diaphragms to your slides ready to install for approx $40 each plus shipping (maybe somebody in your part of the world offers the same service ?)

NRP motorcycle carburettor repair specialist
 

It looks like those may need the plastic rings which I had to remove to install the JBMs. Plus they are out of stock, probably forever lol.

I've had this problem for years so I've searched long and hard for better solution.

This is just an idea. Could you use an epoxy to fill the gap maybe JB weld, using  a dam of sorts and build up material and then have it turned on a lathe to the dimension you need if you know someone with a lathe. Just a wild idea.