Mer 500 50 HP 1977 Need Help with fuel pump

[Mercurylips]

I took my upper carb off to find out what is wrong with it. Not getting enough gas for idle. The fuel pump kits I have installed on it all have two check valve diaphragms and the manual shows the use of only one of them. There is one made of thin rubber like the main diaphragm and one made of very thin fiber. They are identical in form. Which do I use. Serial number for the merc is 4907239

 

[Mercurylips]

Here is a link. The fiber part is shown top right.

 

[Mercurylips]

Tried to find help locally and no one knows. I took the lower carb off since it works fine on the lower two cylinders and found both check valve diaphragms installed so I did the same on the top carb. Didn't seem to cure the problem but I need to take it out and run it on a lake.