Well THAT was a waste of time

[injuhneer]

After a fuel pump failure I have been attempting to get my XZ running correctly again.

The symptom is flooding in the front carb. Nice.

I tried a Virago fuel pump as an alternative. It simply produces too much pressure. The floats don't seem able to overcome the pressure. I may insert a regulator later.

Going back to the OEM pump after repair it seems the front carb is flooding. I am thinking it is coming from the vacuum valve on the fuel pump.

After draining the carb bowl I attached a small tank to again check the fuel level. 20mm below the gasket face. Spot on.

Start the engine and within a short time the overflow starts dumping fuel.

It must be coming from the pump.

[injuhneer]

Yep. Perforated diaphragm. 

This part is less than a year old.

I was looking for a source for diaphragm material. It is interesting to me that when I search for DIY materials suppliers in Oz always appear near the top of the list.

Maybe its time to move to Oz.

[Prophet Of Doom]

You know when Aussies talk about diaphragms they mean the other sort that the wifey uses.  Sex mad those Aussies

Hard to believe the Virago is any higher pressure - the valves look identical to XZ550 and most bikes of the era have pumps only mildly stronger than gravity.  Are you sure your valves and o-rings are good (of course you are!).  There's probably something else going on though.  I guess you'll find out after you get a new diaphragm.

Search ebay for "NOS YAMAHA KY-0472F KEYSTER FUEL PUMP REBUILD KIT XZ550"
There's one on there now.  $26

Keyster don't list XZ550 any more so get it while you can

[injuhneer]

Thanks PoD.

The main diaphragms are OK but the kit may be worth acquiring. I have been looking into some films as possible replacements.

It is the bypass valve (looks like an accelerator pump diaphragm) that failed. I made a (temporary) replacement from 1/32" nitrile. It will do well enough for testing.

[kevin g]

I acquired some diaphragm material when I rebuilt the petcock on my '83.  I have searched my records and cannot find the company that I bought from.  It was a gasket company that the material company sent me to located in the upper mid-west, if my memory is good.

[ArrrGeee]

I would do a go kart fuel pump.

https://www.ebay.com/itm/353433251027?epid=1239860263&hash=item524a436cd3:g:wTEAAOSwrh9gXeA0

a couple of members have also used an electric pump.

or if you want to stay on brand. 
yamaha fuel pump.
https://www.ebay.com/itm/133936850215?hash=item1f2f422527:g:TeMAAOSwUqthlDq5