Metering diaphragms ..hooked or not

[Simondo]

Tillotson (and some Walbro) show a hooked and none hooked diaphragm for the same carb. There is also some mis matching in what you get in some carb kits iv found .

Tillotson HS.....


What do we think could be the reason for a hooked diaphragm as there are plenty of carbs (including this one ) that dont use or need a hooked on one.

 

[67L36Driver]

I’ve no real evidence but I suspect that a large displacement saw with a strong crankcase impulse might call for a ‘hooked’ diaphragm to positively close the needle valve.

Pure speculation on my part.