The regulator will unbolt from the engine case if you have the 63FZ...and the diaphragm is right there.

If you have the 63S version it is a different process to take the regulator apart.

Replacing the diaphragm is not a cure all for these engines. I have not replaced a diaphragm in about 10years. It is rare that they need to be replaced. Often the answer is a guy cleans out the regulator while replacing the diaphragm and he thinks the new diaphragm solved his problem. As you found the dist and debris was the problem.

You need to filter your fuel better.

Troy Newman
Team YS