Paul, I've had bad diaphragms in cheap kits but I haven't had them look perfect even on close inspection, but not work. What I have had, is multi-purpose kits with diaphragms that look almost right but will not work in my carburetor. In particular, the fuel pump diaphragms for Walbro WA and WT carburetors have differences in the flap valve placement but otherwise seem to fit. The way you detect this problem is to compare the new diaphragm very carefully with the original one. I suggest you do that with your HDA kit: there are several different HDA models.
