Can't get timing dialed back to tdc

I also checked the vacuum advance diaphragm by pulled the carb end of the vacuum hose and sucking on it and it's leaving like a sieve. Absolutely no suction at all,and yes,I did check the hose for leaks and its holding vacuum fine. After I get the timing issue settled I have to deal with that. Is it easy to replace just the diaphragm?

Funny thing,wouldn't the engine idle rough or stall if the diaphragm is leaking this bad? It idles fine and seems to run fine on the freeway.