Recently I was working on a Kohler 25 HP twin in an Exmark LazerZ mower. It had a Keihin carburetor installed. The accelerator pump was leaking and when I took it apart the diaphragm was shot. I tried to order a new diaphragm and found out that you had to order a kit that cost's $58. I thought that was to much considering it didn't need new linkage and washers. So I decided to see if I could get either the kit cheaper or just the diaphragm. As it turns out the Diaphragm is used on a number of Keihin carburetors and one of them is the CV40 which used to come on a Harley. To make a long story shorter I got one and it works like a champ plus it was only $15.00.
So if if you need to replace the accelerator pump Diaphragm go to your local HD dealer and tell the parts person you want P/N 27361-76A.
Here is what the diaphragm looks like: