I think I may have a solution......
Heres an email back to the place I got it from.
Hi Jennifer,
I ordered it on Ebay.
I'm going to try something that may help. It seems that the plunger with the O-ring doesn't exactly fit tight up against the valve. So I think I'll try 2 options...1 Either bevel the plastic spacer so that the diaphragm sits deeper in the plastic recess to add more pressure to the O-ring sealing the valve. Or 2 push gently on the diaphragm to bend the back plate slightly so it will have the appropriate depth to push up against the valve. I've been looking at this kit out there on the internet and it seems they've slightly changed the position of the O-ring on the plunger. It used to be closer to the tip which would provide more sealing pressure when installed, just like the stock plunger. I'm sending a picture of an identical kit to give you an idea of what I'm talking about. I'll try and see if I can make it work and get back to you guys so at least you have an idea if it can be fitted. If I install the stock diaphragm it seals no problem. Just after a while it starts leaking through the vacuum hose to #4 cylinder(hence I bought the rebuild kit). The stock plunger has the 0-ring very close to the top of the plunger so it has enough pressure to seal the valve. I have to wait unfortunately since I have too much fuel in the tank right now to take the petcock out but I should have enough out in the next 2 days or so and will let you know how it goes so if you have another customer with the same problem you can suggest one of the solutions I'm trying. I've installed these K&L petcock rebuild kits on a few different bikes and usually they are a no brainer, maybe this kit just needs a little fiddling with. Thanks Jennifer,