'80 KZ 440 vacuum piston diaphragm repair?

My '79 kz400 had Keihin CV34 carbs with the diaphrams (looks like your picture). My '82 kz750 Ltd has the same CV34 carbs...just 4 instead of two. I had problems with my kz400 and it turned out to be the diaphram. The PO had tried to repair the tear, but it didn't work. Went to a bone yard and got one for $30.

Good luck.

On the third try, and after reading some industrial adhesives literature, I came accross a family of adhesives that include regular super glue, and polyurethane adhesives. You may know the polyurethane adhesives under "Gorilla Glue" or Elmer's "Probond". These guys have di-isocyanates in them and can be particularly nasty, but cyanoacrylates and di-isocyanates are one of the only suitable bonding materials for nitrile rubber, or even hydrogenated n butyl rubbers (the green o rings used in r134 ac systems). And speaking of HNBR (the green rubber), I wish people would push keihin and mikuni and the like to use that stuff in carbs. When you look at what they resist and the temps and pressures they resist, they are CLEARLY the choice for using in a casty gasoline / solvent environment especially where there is heat involved.... But I digress. So gorilla glue is your best bet. Superglue cures too stiff, and will degrade over time with humidity (crazy huh?). The gorilla glue, being a polyurethane and using the chemicals it does to react with the bonded surfaces, won't let go even when covered with gasoline or carb cleaner. It remains somewhat flexible, but of course is much stiffer than your diaphragm which is just a nitrile rubber coated cloth. You can apply it thinly over tears and cracks and holes and it's not going to let go.

Last year I was experiencing some pretty bad running conditions, hard starting, stalling, running pretty rough in general. I decided to get the bike back on the road and thought I'd start with a fuel system clean up. After opening the carbs I found a nice tear in the vacuum piston diaphragm. Called up the local shop and it's a $250 part! I did a little searching online and found it for a bit less than $200, but it's still way too much for this cheap old bike. Checked on ebay for a junker set to pull apart, but it looks like the 440 was only offered for a short run and there aren't a lot of them out there.

I was wondering if anyone has ever successfully repaired a tear in that diaphragm? I know it's a long shot and may not be a good long-term fix... any other ideas for finding a old weird part like this? I could spend $50. But much more than that is to much.

The carbs are keihin and they have 1241 and SA25 stamped on them. Any help is appreciated greatly.